diff --git a/assignment-client/src/entities/EntityTreeHeadlessViewer.cpp b/assignment-client/src/entities/EntityTreeHeadlessViewer.cpp
index 3649cf1129..5f43627763 100644
--- a/assignment-client/src/entities/EntityTreeHeadlessViewer.cpp
+++ b/assignment-client/src/entities/EntityTreeHeadlessViewer.cpp
@@ -37,6 +37,7 @@ void EntityTreeHeadlessViewer::update() {
     if (_tree) {
         EntityTreePointer tree = std::static_pointer_cast<EntityTree>(_tree);
         tree->withTryWriteLock([&] {
+            tree->preUpdate();
             tree->update();
         });
     }
diff --git a/interface/src/Application.cpp b/interface/src/Application.cpp
index bf9df95ac0..ef1ab23e1b 100644
--- a/interface/src/Application.cpp
+++ b/interface/src/Application.cpp
@@ -2790,21 +2790,15 @@ Application::~Application() {
     // remove avatars from physics engine
     auto avatarManager = DependencyManager::get<AvatarManager>();
     avatarManager->clearOtherAvatars();
+    auto myCharacterController = getMyAvatar()->getCharacterController();
+    myCharacterController->clearDetailedMotionStates();
 
     PhysicsEngine::Transaction transaction;
     avatarManager->buildPhysicsTransaction(transaction);
     _physicsEngine->processTransaction(transaction);
     avatarManager->handleProcessedPhysicsTransaction(transaction);
-
     avatarManager->deleteAllAvatars();
 
-    auto myCharacterController = getMyAvatar()->getCharacterController();
-    myCharacterController->clearDetailedMotionStates();
-
-    myCharacterController->buildPhysicsTransaction(transaction);
-    _physicsEngine->processTransaction(transaction);
-    myCharacterController->handleProcessedPhysicsTransaction(transaction);
-
     _physicsEngine->setCharacterController(nullptr);
 
     // the _shapeManager should have zero references
@@ -6414,64 +6408,42 @@ void Application::update(float deltaTime) {
         PROFILE_RANGE(simulation_physics, "Simulation");
         PerformanceTimer perfTimer("simulation");
 
-        if (_physicsEnabled) {
-            auto t0 = std::chrono::high_resolution_clock::now();
-            auto t1 = t0;
+        getEntities()->preUpdate();
+
+        auto t0 = std::chrono::high_resolution_clock::now();
+        auto t1 = t0;
+        {
+            PROFILE_RANGE(simulation_physics, "PrePhysics");
+            PerformanceTimer perfTimer("prePhysics)");
             {
-                PROFILE_RANGE(simulation_physics, "PrePhysics");
-                PerformanceTimer perfTimer("prePhysics)");
-                {
-                    PROFILE_RANGE(simulation_physics, "RemoveEntities");
-                    const VectorOfMotionStates& motionStates = _entitySimulation->getObjectsToRemoveFromPhysics();
-                    {
-                        PROFILE_RANGE_EX(simulation_physics, "NumObjs", 0xffff0000, (uint64_t)motionStates.size());
-                        _physicsEngine->removeObjects(motionStates);
-                    }
-                    _entitySimulation->deleteObjectsRemovedFromPhysics();
-                }
+                PROFILE_RANGE(simulation_physics, "Entities");
+                PhysicsEngine::Transaction transaction;
+                _entitySimulation->buildPhysicsTransaction(transaction);
+                _physicsEngine->processTransaction(transaction);
+                _entitySimulation->handleProcessedPhysicsTransaction(transaction);
+            }
 
-                {
-                    PROFILE_RANGE(simulation_physics, "AddEntities");
-                    VectorOfMotionStates motionStates;
-                    getEntities()->getTree()->withReadLock([&] {
-                        _entitySimulation->getObjectsToAddToPhysics(motionStates);
-                        PROFILE_RANGE_EX(simulation_physics, "NumObjs", 0xffff0000, (uint64_t)motionStates.size());
-                        _physicsEngine->addObjects(motionStates);
-                    });
-                }
-                {
-                    VectorOfMotionStates motionStates;
-                    PROFILE_RANGE(simulation_physics, "ChangeEntities");
-                    getEntities()->getTree()->withReadLock([&] {
-                        _entitySimulation->getObjectsToChange(motionStates);
-                        VectorOfMotionStates stillNeedChange = _physicsEngine->changeObjects(motionStates);
-                        _entitySimulation->setObjectsToChange(stillNeedChange);
-                    });
-                }
+            t1 = std::chrono::high_resolution_clock::now();
 
+            {
+                PROFILE_RANGE(simulation_physics, "Avatars");
+                PhysicsEngine::Transaction transaction;
+                avatarManager->buildPhysicsTransaction(transaction);
+                _physicsEngine->processTransaction(transaction);
+                avatarManager->handleProcessedPhysicsTransaction(transaction);
+
+                myAvatar->prepareForPhysicsSimulation();
+                _physicsEngine->enableGlobalContactAddedCallback(myAvatar->isFlying());
+            }
+        }
+
+        if (_physicsEnabled) {
+            {
+                PROFILE_RANGE(simulation_physics, "PrepareActions");
                 _entitySimulation->applyDynamicChanges();
-
-                t1 = std::chrono::high_resolution_clock::now();
-
-                {
-                    PROFILE_RANGE(simulation_physics, "Avatars");
-                    PhysicsEngine::Transaction transaction;
-                    avatarManager->buildPhysicsTransaction(transaction);
-                    _physicsEngine->processTransaction(transaction);
-                    avatarManager->handleProcessedPhysicsTransaction(transaction);
-                    myAvatar->getCharacterController()->buildPhysicsTransaction(transaction);
-                    _physicsEngine->processTransaction(transaction);
-                    myAvatar->getCharacterController()->handleProcessedPhysicsTransaction(transaction);
-                    myAvatar->prepareForPhysicsSimulation();
-                    _physicsEngine->enableGlobalContactAddedCallback(myAvatar->isFlying());
-                }
-
-                {
-                    PROFILE_RANGE(simulation_physics, "PrepareActions");
-                    _physicsEngine->forEachDynamic([&](EntityDynamicPointer dynamic) {
-                        dynamic->prepareForPhysicsSimulation();
-                    });
-                }
+                _physicsEngine->forEachDynamic([&](EntityDynamicPointer dynamic) {
+                    dynamic->prepareForPhysicsSimulation();
+                });
             }
             auto t2 = std::chrono::high_resolution_clock::now();
             {
diff --git a/interface/src/avatar/AvatarManager.cpp b/interface/src/avatar/AvatarManager.cpp
index 00e743312f..e01f9339f4 100755
--- a/interface/src/avatar/AvatarManager.cpp
+++ b/interface/src/avatar/AvatarManager.cpp
@@ -101,7 +101,7 @@ AvatarSharedPointer AvatarManager::addAvatar(const QUuid& sessionUUID, const QWe
 }
 
 AvatarManager::~AvatarManager() {
-    assert(_avatarsToChangeInPhysics.empty());
+    assert(_otherAvatarsToChangeInPhysics.empty());
 }
 
 void AvatarManager::init() {
@@ -295,7 +295,7 @@ void AvatarManager::updateOtherAvatars(float deltaTime) {
 
     render::Transaction renderTransaction;
     workload::Transaction workloadTransaction;
- 
+
     for (int p = kHero; p < NumVariants; p++) {
         auto& priorityQueue = avatarPriorityQueues[p];
         // Sorting the current queue HERE as part of the measured timing.
@@ -314,7 +314,7 @@ void AvatarManager::updateOtherAvatars(float deltaTime) {
                 // remove the orb if it is there
                 avatar->removeOrb();
                 if (avatar->needsPhysicsUpdate()) {
-                    _avatarsToChangeInPhysics.insert(avatar);
+                    _otherAvatarsToChangeInPhysics.insert(avatar);
                 }
             } else {
                 avatar->updateOrbPosition();
@@ -419,69 +419,111 @@ AvatarSharedPointer AvatarManager::newSharedAvatar(const QUuid& sessionUUID) {
 }
 
 void AvatarManager::queuePhysicsChange(const OtherAvatarPointer& avatar) {
-    _avatarsToChangeInPhysics.insert(avatar);
+    _otherAvatarsToChangeInPhysics.insert(avatar);
+}
+
+DetailedMotionState* AvatarManager::createDetailedMotionState(OtherAvatarPointer avatar, int32_t jointIndex) {
+    bool isBound = false;
+    std::vector<int32_t> boundJoints;
+    const btCollisionShape* shape = avatar->createCollisionShape(jointIndex, isBound, boundJoints);
+    if (shape) {
+        DetailedMotionState* motionState = new DetailedMotionState(avatar, shape, jointIndex);
+        motionState->setMass(0.0f); // DetailedMotionState has KINEMATIC MotionType, so zero mass is ok
+        motionState->setIsBound(isBound, boundJoints);
+        return motionState;
+    }
+    return nullptr;
+}
+
+void AvatarManager::rebuildAvatarPhysics(PhysicsEngine::Transaction& transaction, OtherAvatarPointer avatar) {
+    if (!avatar->_motionState) {
+        avatar->_motionState = new AvatarMotionState(avatar, nullptr);
+    }
+    AvatarMotionState* motionState = avatar->_motionState;
+    ShapeInfo shapeInfo;
+    avatar->computeShapeInfo(shapeInfo);
+    const btCollisionShape* shape = ObjectMotionState::getShapeManager()->getShape(shapeInfo);
+    assert(shape);
+    motionState->setShape(shape);
+    motionState->setMass(avatar->computeMass());
+    if (motionState->getRigidBody()) {
+        transaction.objectsToReinsert.push_back(motionState);
+    } else {
+        transaction.objectsToAdd.push_back(motionState);
+    }
+    motionState->clearIncomingDirtyFlags();
+
+    // Rather than reconcile numbers of joints after change to model or LOD
+    // we blow away old detailedMotionStates and create anew all around.
+
+    // delete old detailedMotionStates
+    auto& detailedMotionStates = avatar->getDetailedMotionStates();
+    if (detailedMotionStates.size() != 0) {
+        for (auto& detailedMotionState : detailedMotionStates) {
+            transaction.objectsToRemove.push_back(detailedMotionState);
+        }
+        avatar->resetDetailedMotionStates();
+    }
+
+    // build new detailedMotionStates
+    OtherAvatar::BodyLOD lod = avatar->getBodyLOD();
+    if (lod == OtherAvatar::BodyLOD::Sphere) {
+        auto dMotionState = createDetailedMotionState(avatar, -1);
+        if (dMotionState) {
+            detailedMotionStates.push_back(dMotionState);
+            transaction.objectsToAdd.push_back(dMotionState);
+        }
+    } else {
+        int32_t numJoints = avatar->getJointCount();
+        for (int32_t i = 0; i < numJoints; i++) {
+            auto dMotionState = createDetailedMotionState(avatar, i);
+            if (dMotionState) {
+                detailedMotionStates.push_back(dMotionState);
+                transaction.objectsToAdd.push_back(dMotionState);
+            }
+        }
+    }
+    avatar->_needsReinsertion = false;
 }
 
 void AvatarManager::buildPhysicsTransaction(PhysicsEngine::Transaction& transaction) {
-    SetOfOtherAvatars failedShapeBuilds;
-    for (auto avatar : _avatarsToChangeInPhysics) {
+    _myAvatar->getCharacterController()->buildPhysicsTransaction(transaction);
+    for (auto avatar : _otherAvatarsToChangeInPhysics) {
         bool isInPhysics = avatar->isInPhysicsSimulation();
         if (isInPhysics != avatar->shouldBeInPhysicsSimulation()) {
             if (isInPhysics) {
                 transaction.objectsToRemove.push_back(avatar->_motionState);
                 avatar->_motionState = nullptr;
                 auto& detailedMotionStates = avatar->getDetailedMotionStates();
-                for (auto& mState : detailedMotionStates) {
-                    transaction.objectsToRemove.push_back(mState);
+                for (auto& motionState : detailedMotionStates) {
+                    transaction.objectsToRemove.push_back(motionState);
                 }
                 avatar->resetDetailedMotionStates();
             } else {
-                if (avatar->getDetailedMotionStates().size() == 0) {
-                    avatar->createDetailedMotionStates(avatar);
-                    for (auto dMotionState : avatar->getDetailedMotionStates()) {
-                        transaction.objectsToAdd.push_back(dMotionState);
-                    }
-                }
-                if (avatar->getDetailedMotionStates().size() > 0) {
-                    ShapeInfo shapeInfo;
-                    avatar->computeShapeInfo(shapeInfo);
-                    btCollisionShape* shape = const_cast<btCollisionShape*>(ObjectMotionState::getShapeManager()->getShape(shapeInfo));
-                    if (shape) {
-                        AvatarMotionState* motionState = new AvatarMotionState(avatar, shape);
-                        motionState->setMass(avatar->computeMass());
-                        avatar->_motionState = motionState;
-                        transaction.objectsToAdd.push_back(motionState);
-                    } else {
-                        failedShapeBuilds.insert(avatar);
-                    }
-                } else {
-                    failedShapeBuilds.insert(avatar);
-                }
+                rebuildAvatarPhysics(transaction, avatar);
             }
         } else if (isInPhysics) {
-            transaction.objectsToChange.push_back(avatar->_motionState);
-            
-            auto& detailedMotionStates = avatar->getDetailedMotionStates();
-            for (auto& mState : detailedMotionStates) {
-                if (mState) {
-                    transaction.objectsToChange.push_back(mState);
-                }
+            AvatarMotionState* motionState = avatar->_motionState;
+            uint32_t flags = motionState->getIncomingDirtyFlags();
+            if (flags & EASY_DIRTY_PHYSICS_FLAGS) {
+                motionState->handleEasyChanges(flags);
+            }
+            // NOTE: we don't call detailedMotionState->handleEasyChanges() here because they are KINEMATIC
+            // and Bullet will automagically call DetailedMotionState::getWorldTransform() on all that are active.
+
+            if (motionState->needsNewShape()) {
+                rebuildAvatarPhysics(transaction, avatar);
+            } else {
+                if (flags & (Simulation::DIRTY_MOTION_TYPE | Simulation::DIRTY_COLLISION_GROUP)) {
+                    transaction.objectsToReinsert.push_back(motionState);
+                }
+                motionState->clearIncomingDirtyFlags();
             }
-            
         }
     }
-    _avatarsToChangeInPhysics.swap(failedShapeBuilds);
 }
 
 void AvatarManager::handleProcessedPhysicsTransaction(PhysicsEngine::Transaction& transaction) {
-    // things on objectsToChange correspond to failed changes
-    // so we push them back onto _avatarsToChangeInPhysics
-    for (auto object : transaction.objectsToChange) {
-        AvatarMotionState* motionState = static_cast<AvatarMotionState*>(object);
-        assert(motionState);
-        assert(motionState->_avatar);
-        _avatarsToChangeInPhysics.insert(motionState->_avatar);
-    }
     // things on objectsToRemove are ready for delete
     for (auto object : transaction.objectsToRemove) {
         delete object;
@@ -570,7 +612,7 @@ void AvatarManager::clearOtherAvatars() {
                 ++avatarIterator;
             }
         }
-    }    
+    }
 
     for (auto& av : removedAvatars) {
         handleRemovedAvatar(av);
@@ -578,7 +620,7 @@ void AvatarManager::clearOtherAvatars() {
 }
 
 void AvatarManager::deleteAllAvatars() {
-    assert(_avatarsToChangeInPhysics.empty());
+    assert(_otherAvatarsToChangeInPhysics.empty());
     QReadLocker locker(&_hashLock);
     AvatarHash::iterator avatarIterator = _avatarHash.begin();
     while (avatarIterator != _avatarHash.end()) {
@@ -588,7 +630,7 @@ void AvatarManager::deleteAllAvatars() {
         if (avatar != _myAvatar) {
             auto otherAvatar = std::static_pointer_cast<OtherAvatar>(avatar);
             assert(!otherAvatar->_motionState);
-            assert(otherAvatar->getDetailedMotionStates().size() == 0);            
+            assert(otherAvatar->getDetailedMotionStates().size() == 0);
         }
     }
 }
diff --git a/interface/src/avatar/AvatarManager.h b/interface/src/avatar/AvatarManager.h
index 98deebe919..db1bc125a4 100644
--- a/interface/src/avatar/AvatarManager.h
+++ b/interface/src/avatar/AvatarManager.h
@@ -273,6 +273,8 @@ public slots:
 
 protected:
     AvatarSharedPointer addAvatar(const QUuid& sessionUUID, const QWeakPointer<Node>& mixerWeakPointer) override;
+    DetailedMotionState* createDetailedMotionState(OtherAvatarPointer avatar, int32_t jointIndex);
+    void rebuildAvatarPhysics(PhysicsEngine::Transaction& transaction, OtherAvatarPointer avatar);
 
 private:
     explicit AvatarManager(QObject* parent = 0);
@@ -288,7 +290,7 @@ private:
     void handleTransitAnimations(AvatarTransit::Status status);
 
     using SetOfOtherAvatars = std::set<OtherAvatarPointer>;
-    SetOfOtherAvatars _avatarsToChangeInPhysics;
+    SetOfOtherAvatars _otherAvatarsToChangeInPhysics;
 
     std::shared_ptr<MyAvatar> _myAvatar;
     quint64 _lastSendAvatarDataTime = 0; // Controls MyAvatar send data rate.
diff --git a/interface/src/avatar/AvatarMotionState.cpp b/interface/src/avatar/AvatarMotionState.cpp
index 77fc81fa04..97085c8443 100755
--- a/interface/src/avatar/AvatarMotionState.cpp
+++ b/interface/src/avatar/AvatarMotionState.cpp
@@ -29,23 +29,19 @@ void AvatarMotionState::handleEasyChanges(uint32_t& flags) {
     }
 }
 
-bool AvatarMotionState::handleHardAndEasyChanges(uint32_t& flags, PhysicsEngine* engine) {
-    return ObjectMotionState::handleHardAndEasyChanges(flags, engine);
-}
-
 AvatarMotionState::~AvatarMotionState() {
     assert(_avatar);
     _avatar = nullptr;
 }
 
 // virtual
-uint32_t AvatarMotionState::getIncomingDirtyFlags() {
+uint32_t AvatarMotionState::getIncomingDirtyFlags() const {
     return _body ? _dirtyFlags : 0;
 }
 
-void AvatarMotionState::clearIncomingDirtyFlags() {
+void AvatarMotionState::clearIncomingDirtyFlags(uint32_t mask) {
     if (_body) {
-        _dirtyFlags = 0;
+        _dirtyFlags &= ~mask;
     }
 }
 
@@ -54,13 +50,6 @@ PhysicsMotionType AvatarMotionState::computePhysicsMotionType() const {
     return MOTION_TYPE_DYNAMIC;
 }
 
-// virtual and protected
-const btCollisionShape* AvatarMotionState::computeNewShape() {
-    ShapeInfo shapeInfo;
-    _avatar->computeShapeInfo(shapeInfo);
-    return getShapeManager()->getShape(shapeInfo);
-}
-
 // virtual
 bool AvatarMotionState::isMoving() const {
     return false;
diff --git a/interface/src/avatar/AvatarMotionState.h b/interface/src/avatar/AvatarMotionState.h
index 3103341622..a752d2c8fb 100644
--- a/interface/src/avatar/AvatarMotionState.h
+++ b/interface/src/avatar/AvatarMotionState.h
@@ -23,44 +23,44 @@ class AvatarMotionState : public ObjectMotionState {
 public:
     AvatarMotionState(OtherAvatarPointer avatar, const btCollisionShape* shape);
 
-    virtual void handleEasyChanges(uint32_t& flags) override;
-    virtual bool handleHardAndEasyChanges(uint32_t& flags, PhysicsEngine* engine) override;
+    void handleEasyChanges(uint32_t& flags) override;
 
-    virtual PhysicsMotionType getMotionType() const override { return _motionType; }
+    PhysicsMotionType getMotionType() const override { return _motionType; }
 
-    virtual uint32_t getIncomingDirtyFlags() override;
-    virtual void clearIncomingDirtyFlags() override;
+    uint32_t getIncomingDirtyFlags() const override;
+    void clearIncomingDirtyFlags(uint32_t mask = DIRTY_PHYSICS_FLAGS) override;
 
-    virtual PhysicsMotionType computePhysicsMotionType() const override;
+    PhysicsMotionType computePhysicsMotionType() const override;
 
-    virtual bool isMoving() const override;
+    bool isMoving() const override;
 
     // this relays incoming position/rotation to the RigidBody
-    virtual void getWorldTransform(btTransform& worldTrans) const override;
+    void getWorldTransform(btTransform& worldTrans) const override;
 
     // this relays outgoing position/rotation to the EntityItem
-    virtual void setWorldTransform(const btTransform& worldTrans) override;
+    void setWorldTransform(const btTransform& worldTrans) override;
 
 
     // These pure virtual methods must be implemented for each MotionState type
     // and make it possible to implement more complicated methods in this base class.
 
     // pure virtual overrides from ObjectMotionState
-    virtual float getObjectRestitution() const override;
-    virtual float getObjectFriction() const override;
-    virtual float getObjectLinearDamping() const override;
-    virtual float getObjectAngularDamping() const override;
+    float getObjectRestitution() const override;
+    float getObjectFriction() const override;
+    float getObjectLinearDamping() const override;
+    float getObjectAngularDamping() const override;
 
-    virtual glm::vec3 getObjectPosition() const override;
-    virtual glm::quat getObjectRotation() const override;
-    virtual glm::vec3 getObjectLinearVelocity() const override;
-    virtual glm::vec3 getObjectAngularVelocity() const override;
-    virtual glm::vec3 getObjectGravity() const override;
+    glm::vec3 getObjectPosition() const override;
+    glm::quat getObjectRotation() const override;
+    glm::vec3 getObjectLinearVelocity() const override;
+    glm::vec3 getObjectAngularVelocity() const override;
+    glm::vec3 getObjectGravity() const override;
 
-    virtual const QUuid getObjectID() const override;
+    const QUuid getObjectID() const override;
 
-    virtual QString getName() const override;
-    virtual QUuid getSimulatorID() const override;
+    QString getName() const override;
+    ShapeType getShapeType() const override { return SHAPE_TYPE_CAPSULE_Y; }
+    QUuid getSimulatorID() const override;
 
     void setBoundingBox(const glm::vec3& corner, const glm::vec3& diagonal);
 
@@ -69,9 +69,9 @@ public:
     void setCollisionGroup(int32_t group) { _collisionGroup = group; }
     int32_t getCollisionGroup() { return _collisionGroup; }
 
-    virtual void computeCollisionGroupAndMask(int32_t& group, int32_t& mask) const override;
+    void computeCollisionGroupAndMask(int32_t& group, int32_t& mask) const override;
 
-    virtual float getMass() const override;
+    float getMass() const override;
 
     friend class AvatarManager;
     friend class Avatar;
@@ -85,9 +85,6 @@ protected:
     // ever called by the Avatar class dtor.
     ~AvatarMotionState();
 
-    virtual bool isReadyToComputeShape() const override { return true; }
-    virtual const btCollisionShape* computeNewShape() override;
-
     OtherAvatarPointer _avatar;
     float _diameter { 0.0f };
     int32_t _collisionGroup;
diff --git a/interface/src/avatar/DetailedMotionState.cpp b/interface/src/avatar/DetailedMotionState.cpp
index cec27108ca..02a2b9d425 100644
--- a/interface/src/avatar/DetailedMotionState.cpp
+++ b/interface/src/avatar/DetailedMotionState.cpp
@@ -17,7 +17,7 @@
 #include "MyAvatar.h"
 
 
-DetailedMotionState::DetailedMotionState(AvatarPointer avatar, const btCollisionShape* shape, int jointIndex) : 
+DetailedMotionState::DetailedMotionState(AvatarPointer avatar, const btCollisionShape* shape, int32_t jointIndex) : 
     ObjectMotionState(shape), _avatar(avatar), _jointIndex(jointIndex) {
     assert(_avatar);
     if (!_avatar->isMyAvatar()) {
@@ -33,47 +33,26 @@ void DetailedMotionState::handleEasyChanges(uint32_t& flags) {
     }
 }
 
-bool DetailedMotionState::handleHardAndEasyChanges(uint32_t& flags, PhysicsEngine* engine) {
-    return ObjectMotionState::handleHardAndEasyChanges(flags, engine);
-}
-
 DetailedMotionState::~DetailedMotionState() {
     assert(_avatar);
     _avatar = nullptr;
 }
 
 // virtual
-uint32_t DetailedMotionState::getIncomingDirtyFlags() {
+uint32_t DetailedMotionState::getIncomingDirtyFlags() const {
     return _body ? _dirtyFlags : 0;
 }
 
-void DetailedMotionState::clearIncomingDirtyFlags() {
+void DetailedMotionState::clearIncomingDirtyFlags(uint32_t mask) {
     if (_body) {
-        _dirtyFlags = 0;
+        _dirtyFlags &= ~mask;
     }
 }
 
 PhysicsMotionType DetailedMotionState::computePhysicsMotionType() const {
-    // TODO?: support non-DYNAMIC motion for avatars? (e.g. when sitting)
     return MOTION_TYPE_KINEMATIC;
 }
 
-// virtual and protected
-const btCollisionShape* DetailedMotionState::computeNewShape() {
-    btCollisionShape* shape = nullptr;
-    if (!_avatar->isMyAvatar()) {
-        if (_otherAvatar != nullptr) {
-            shape =  _otherAvatar->createCollisionShape(_jointIndex, _isBound, _boundJoints);
-        }
-    } else {
-        std::shared_ptr<MyAvatar> myAvatar = std::static_pointer_cast<MyAvatar>(_avatar);
-        if (myAvatar) {
-            shape = myAvatar->getCharacterController()->createDetailedCollisionShapeForJoint(_jointIndex);
-        }
-    }
-    return shape;
-}
-
 // virtual
 bool DetailedMotionState::isMoving() const {
     return false;
@@ -178,11 +157,23 @@ void DetailedMotionState::setRigidBody(btRigidBody* body) {
 }
 
 void DetailedMotionState::setShape(const btCollisionShape* shape) {
-    ObjectMotionState::setShape(shape);
+    if (_shape != shape) {
+        if (_shape) {
+            getShapeManager()->releaseShape(_shape);
+        }
+        _shape = shape;
+        if (_body) {
+            assert(_shape);
+            _body->setCollisionShape(const_cast<btCollisionShape*>(_shape));
+        }
+    } else if (shape) {
+        // we need to release unused reference to shape
+        getShapeManager()->releaseShape(shape);
+    }
 }
 
 void DetailedMotionState::forceActive() {
     if (_body && !_body->isActive()) {
         _body->setActivationState(ACTIVE_TAG);
     }
-}
\ No newline at end of file
+}
diff --git a/interface/src/avatar/DetailedMotionState.h b/interface/src/avatar/DetailedMotionState.h
index a9b4b4bb64..de59f41310 100644
--- a/interface/src/avatar/DetailedMotionState.h
+++ b/interface/src/avatar/DetailedMotionState.h
@@ -23,55 +23,55 @@ class DetailedMotionState : public ObjectMotionState {
 public:
     DetailedMotionState(AvatarPointer avatar, const btCollisionShape* shape, int jointIndex);
 
-    virtual void handleEasyChanges(uint32_t& flags) override;
-    virtual bool handleHardAndEasyChanges(uint32_t& flags, PhysicsEngine* engine) override;
+    void handleEasyChanges(uint32_t& flags) override;
 
-    virtual PhysicsMotionType getMotionType() const override { return _motionType; }
+    PhysicsMotionType getMotionType() const override { return _motionType; }
 
-    virtual uint32_t getIncomingDirtyFlags() override;
-    virtual void clearIncomingDirtyFlags() override;
+    uint32_t getIncomingDirtyFlags() const override;
+    void clearIncomingDirtyFlags(uint32_t mask = DIRTY_PHYSICS_FLAGS) override;
 
-    virtual PhysicsMotionType computePhysicsMotionType() const override;
+    PhysicsMotionType computePhysicsMotionType() const override;
 
-    virtual bool isMoving() const override;
+    bool isMoving() const override;
 
     // this relays incoming position/rotation to the RigidBody
-    virtual void getWorldTransform(btTransform& worldTrans) const override;
+    void getWorldTransform(btTransform& worldTrans) const override;
 
     // this relays outgoing position/rotation to the EntityItem
-    virtual void setWorldTransform(const btTransform& worldTrans) override;
+    void setWorldTransform(const btTransform& worldTrans) override;
 
 
     // These pure virtual methods must be implemented for each MotionState type
     // and make it possible to implement more complicated methods in this base class.
 
     // pure virtual overrides from ObjectMotionState
-    virtual float getObjectRestitution() const override;
-    virtual float getObjectFriction() const override;
-    virtual float getObjectLinearDamping() const override;
-    virtual float getObjectAngularDamping() const override;
+    float getObjectRestitution() const override;
+    float getObjectFriction() const override;
+    float getObjectLinearDamping() const override;
+    float getObjectAngularDamping() const override;
 
-    virtual glm::vec3 getObjectPosition() const override;
-    virtual glm::quat getObjectRotation() const override;
-    virtual glm::vec3 getObjectLinearVelocity() const override;
-    virtual glm::vec3 getObjectAngularVelocity() const override;
-    virtual glm::vec3 getObjectGravity() const override;
+    glm::vec3 getObjectPosition() const override;
+    glm::quat getObjectRotation() const override;
+    glm::vec3 getObjectLinearVelocity() const override;
+    glm::vec3 getObjectAngularVelocity() const override;
+    glm::vec3 getObjectGravity() const override;
 
-    virtual const QUuid getObjectID() const override;
+    const QUuid getObjectID() const override;
 
-    virtual QString getName() const override;
-    virtual QUuid getSimulatorID() const override;
+    QString getName() const override;
+    ShapeType getShapeType() const override { return SHAPE_TYPE_HULL; }
+    QUuid getSimulatorID() const override;
 
     void addDirtyFlags(uint32_t flags) { _dirtyFlags |= flags; }
 
-    virtual void computeCollisionGroupAndMask(int32_t& group, int32_t& mask) const override;
+    void computeCollisionGroupAndMask(int32_t& group, int32_t& mask) const override;
 
-    virtual float getMass() const override;
+    float getMass() const override;
     void forceActive();
     QUuid getAvatarID() const { return _avatar->getID(); }
-    int getJointIndex() const { return _jointIndex; }
-    void setIsBound(bool isBound, std::vector<int> boundJoints) { _isBound = isBound; _boundJoints = boundJoints; }
-    bool getIsBound(std::vector<int>& boundJoints) const { boundJoints = _boundJoints; return _isBound; }
+    int32_t getJointIndex() const { return _jointIndex; }
+    void setIsBound(bool isBound, const std::vector<int32_t>& boundJoints) { _isBound = isBound; _boundJoints = boundJoints; }
+    bool getIsBound(std::vector<int32_t>& boundJoints) const { boundJoints = _boundJoints; return _isBound; }
 
     friend class AvatarManager;
     friend class Avatar;
@@ -84,17 +84,14 @@ protected:
     // ever called by the Avatar class dtor.
     ~DetailedMotionState();
 
-    virtual bool isReadyToComputeShape() const override { return true; }
-    virtual const btCollisionShape* computeNewShape() override;
-
     AvatarPointer _avatar;
     float _diameter { 0.0f };
 
     uint32_t _dirtyFlags;
-    int _jointIndex { -1 };
+    int32_t _jointIndex { -1 };
     OtherAvatarPointer _otherAvatar { nullptr };
     bool _isBound { false };
-    std::vector<int> _boundJoints;
+    std::vector<int32_t> _boundJoints;
 };
 
 #endif // hifi_DetailedMotionState_h
diff --git a/interface/src/avatar/MyCharacterController.cpp b/interface/src/avatar/MyCharacterController.cpp
index b0123abe8d..aef1bcd668 100755
--- a/interface/src/avatar/MyCharacterController.cpp
+++ b/interface/src/avatar/MyCharacterController.cpp
@@ -377,21 +377,18 @@ void MyCharacterController::updateMassProperties() {
     _rigidBody->setMassProps(mass, inertia);
 }
 
-btCollisionShape* MyCharacterController::createDetailedCollisionShapeForJoint(int jointIndex) {
+const btCollisionShape* MyCharacterController::createDetailedCollisionShapeForJoint(int32_t jointIndex) {
     ShapeInfo shapeInfo;
     _avatar->computeDetailedShapeInfo(shapeInfo, jointIndex);
     if (shapeInfo.getType() != SHAPE_TYPE_NONE) {
-        btCollisionShape* shape = const_cast<btCollisionShape*>(ObjectMotionState::getShapeManager()->getShape(shapeInfo));
-        if (shape) {
-            shape->setMargin(0.001f);
-        }
+        const btCollisionShape* shape = ObjectMotionState::getShapeManager()->getShape(shapeInfo);
         return shape;
     }
     return nullptr;
 }
 
-DetailedMotionState* MyCharacterController::createDetailedMotionStateForJoint(int jointIndex) {
-    auto shape = createDetailedCollisionShapeForJoint(jointIndex);
+DetailedMotionState* MyCharacterController::createDetailedMotionStateForJoint(int32_t jointIndex) {
+    const btCollisionShape* shape = createDetailedCollisionShapeForJoint(jointIndex);
     if (shape) {
         DetailedMotionState* motionState = new DetailedMotionState(_avatar, shape, jointIndex);
         motionState->setMass(_avatar->computeMass());
@@ -423,25 +420,16 @@ void MyCharacterController::buildPhysicsTransaction(PhysicsEngine::Transaction&
     }
     if (_pendingFlags & PENDING_FLAG_ADD_DETAILED_TO_SIMULATION) {
         _pendingFlags &= ~PENDING_FLAG_ADD_DETAILED_TO_SIMULATION;
-        for (int i = 0; i < _avatar->getJointCount(); i++) {
+        for (int32_t i = 0; i < _avatar->getJointCount(); i++) {
             auto dMotionState = createDetailedMotionStateForJoint(i);
             if (dMotionState) {
                 _detailedMotionStates.push_back(dMotionState);
                 transaction.objectsToAdd.push_back(dMotionState);
             }
         }
-    } 
-}
-
-void MyCharacterController::handleProcessedPhysicsTransaction(PhysicsEngine::Transaction& transaction) {
-    // things on objectsToRemove are ready for delete
-    for (auto object : transaction.objectsToRemove) {
-        delete object;
     }
-    transaction.clear();
 }
 
-
 class DetailedRayResultCallback : public btCollisionWorld::AllHitsRayResultCallback {
 public:
     DetailedRayResultCallback()
@@ -467,7 +455,7 @@ std::vector<MyCharacterController::RayAvatarResult> MyCharacterController::rayTe
         _dynamicsWorld->rayTest(origin, end, rayCallback);
         if (rayCallback.m_hitFractions.size() > 0) {
             foundAvatars.reserve(rayCallback.m_hitFractions.size());
-            for (int i = 0; i < rayCallback.m_hitFractions.size(); i++) {
+            for (int32_t i = 0; i < rayCallback.m_hitFractions.size(); i++) {
                 auto object = rayCallback.m_collisionObjects[i];
                 ObjectMotionState* motionState = static_cast<ObjectMotionState*>(object->getUserPointer());
                 if (motionState && motionState->getType() == MOTIONSTATE_TYPE_DETAILED) {
@@ -493,4 +481,4 @@ std::vector<MyCharacterController::RayAvatarResult> MyCharacterController::rayTe
         }
     }
     return foundAvatars;
-}
\ No newline at end of file
+}
diff --git a/interface/src/avatar/MyCharacterController.h b/interface/src/avatar/MyCharacterController.h
index f861f82422..0b64f66850 100644
--- a/interface/src/avatar/MyCharacterController.h
+++ b/interface/src/avatar/MyCharacterController.h
@@ -44,27 +44,25 @@ public:
 
     void setDensity(btScalar density) { _density = density; }
 
-    btCollisionShape* createDetailedCollisionShapeForJoint(int jointIndex);
-    DetailedMotionState* createDetailedMotionStateForJoint(int jointIndex);
+    const btCollisionShape* createDetailedCollisionShapeForJoint(int32_t jointIndex);
+    DetailedMotionState* createDetailedMotionStateForJoint(int32_t jointIndex);
     std::vector<DetailedMotionState*>& getDetailedMotionStates() { return _detailedMotionStates; }
     void clearDetailedMotionStates();
     void resetDetailedMotionStates();
 
     void buildPhysicsTransaction(PhysicsEngine::Transaction& transaction);
-    void handleProcessedPhysicsTransaction(PhysicsEngine::Transaction& transaction);
-
 
     struct RayAvatarResult {
         bool _intersect { false };
         bool _isBound { false };
         QUuid _intersectWithAvatar;
-        int _intersectWithJoint { -1 };
+        int32_t _intersectWithJoint { -1 };
         float _distance { 0.0f };
         float _maxDistance { 0.0f };
         QVariantMap _extraInfo;
         glm::vec3 _intersectionPoint;
         glm::vec3 _intersectionNormal;
-        std::vector<int> _boundJoints;
+        std::vector<int32_t> _boundJoints;
     };
     std::vector<RayAvatarResult> rayTest(const btVector3& origin, const btVector3& direction, const btScalar& length,
                                          const QVector<uint>& jointsToExclude) const;
diff --git a/interface/src/avatar/OtherAvatar.cpp b/interface/src/avatar/OtherAvatar.cpp
index d8cfe8f107..107932d5ec 100755
--- a/interface/src/avatar/OtherAvatar.cpp
+++ b/interface/src/avatar/OtherAvatar.cpp
@@ -116,6 +116,8 @@ void OtherAvatar::updateSpaceProxy(workload::Transaction& transaction) const {
 int OtherAvatar::parseDataFromBuffer(const QByteArray& buffer) {
     int32_t bytesRead = Avatar::parseDataFromBuffer(buffer);
     for (size_t i = 0; i < _detailedMotionStates.size(); i++) {
+        // NOTE: we activate _detailedMotionStates is because they are KINEMATIC
+        // and Bullet will automagically call DetailedMotionState::getWorldTransform() when active.
         _detailedMotionStates[i]->forceActive();
     }
     if (_moving && _motionState) {
@@ -124,11 +126,11 @@ int OtherAvatar::parseDataFromBuffer(const QByteArray& buffer) {
     return bytesRead;
 }
 
-btCollisionShape* OtherAvatar::createCollisionShape(int jointIndex, bool& isBound, std::vector<int>& boundJoints) {
+const btCollisionShape* OtherAvatar::createCollisionShape(int32_t jointIndex, bool& isBound, std::vector<int32_t>& boundJoints) {
     ShapeInfo shapeInfo;
     isBound = false;
-    QString jointName = ""; 
-    if (jointIndex > -1 && jointIndex < (int)_multiSphereShapes.size()) {
+    QString jointName = "";
+    if (jointIndex > -1 && jointIndex < (int32_t)_multiSphereShapes.size()) {
         jointName = _multiSphereShapes[jointIndex].getJointName();
     }
     switch (_bodyLOD) {
@@ -163,39 +165,21 @@ btCollisionShape* OtherAvatar::createCollisionShape(int jointIndex, bool& isBoun
             }
             break;
         }
+        // Note: MultiSphereLow case really means: "skip fingers and use spheres for hands,
+        // else fall through to MultiSphereHigh case"
     case BodyLOD::MultiSphereHigh:
         computeDetailedShapeInfo(shapeInfo, jointIndex);
         break;
     default:
+        assert(false); // should never reach here
         break;
     }
-    if (shapeInfo.getType() != SHAPE_TYPE_NONE) {
-        auto shape = const_cast<btCollisionShape*>(ObjectMotionState::getShapeManager()->getShape(shapeInfo));
-        if (shape) {
-            shape->setMargin(0.001f);
-        }
-        return shape;
-    }
-    return nullptr;
-}
-
-DetailedMotionState* OtherAvatar::createMotionState(std::shared_ptr<OtherAvatar> avatar, int jointIndex) {
-    bool isBound = false;
-    std::vector<int> boundJoints;
-    btCollisionShape* shape = createCollisionShape(jointIndex, isBound, boundJoints);
-    if (shape) {
-        DetailedMotionState* motionState = new DetailedMotionState(avatar, shape, jointIndex);
-        motionState->setMass(computeMass());
-        motionState->setIsBound(isBound, boundJoints);
-        return motionState;
-    }
-    return nullptr;
+    return ObjectMotionState::getShapeManager()->getShape(shapeInfo);
 }
 
 void OtherAvatar::resetDetailedMotionStates() {
-    for (size_t i = 0; i < _detailedMotionStates.size(); i++) {
-        _detailedMotionStates[i] = nullptr;
-    }
+    // NOTE: the DetailedMotionStates are deleted after being added to PhysicsEngine::Transaction::_objectsToRemove
+    // See AvatarManager::handleProcessedPhysicsTransaction()
     _detailedMotionStates.clear();
 }
 
@@ -231,11 +215,11 @@ void OtherAvatar::computeShapeLOD() {
 }
 
 bool OtherAvatar::isInPhysicsSimulation() const {
-    return _motionState != nullptr && _detailedMotionStates.size() > 0;
+    return _motionState && _motionState->getRigidBody();
 }
 
 bool OtherAvatar::shouldBeInPhysicsSimulation() const {
-    return !isDead() && !(isInPhysicsSimulation() && _needsReinsertion);
+    return !isDead() && _workloadRegion < workload::Region::R3;
 }
 
 bool OtherAvatar::needsPhysicsUpdate() const {
@@ -245,12 +229,9 @@ bool OtherAvatar::needsPhysicsUpdate() const {
 
 void OtherAvatar::rebuildCollisionShape() {
     if (_motionState) {
+        // do not actually rebuild here, instead flag for later
         _motionState->addDirtyFlags(Simulation::DIRTY_SHAPE | Simulation::DIRTY_MASS);
-    }
-    for (size_t i = 0; i < _detailedMotionStates.size(); i++) {
-        if (_detailedMotionStates[i]) {
-            _detailedMotionStates[i]->addDirtyFlags(Simulation::DIRTY_SHAPE | Simulation::DIRTY_MASS);
-        }
+        _needsReinsertion = true;
     }
 }
 
@@ -260,25 +241,6 @@ void OtherAvatar::setCollisionWithOtherAvatarsFlags() {
     }
 }
 
-void OtherAvatar::createDetailedMotionStates(const std::shared_ptr<OtherAvatar>& avatar) {
-    auto& detailedMotionStates = getDetailedMotionStates();
-    assert(detailedMotionStates.empty());
-    if (_bodyLOD == BodyLOD::Sphere) {
-        auto dMotionState = createMotionState(avatar, -1);
-        if (dMotionState) {
-            detailedMotionStates.push_back(dMotionState);
-        }
-    } else {
-        for (int i = 0; i < getJointCount(); i++) {
-            auto dMotionState = createMotionState(avatar, i);
-            if (dMotionState) {
-                detailedMotionStates.push_back(dMotionState);
-            }
-        }
-    }
-    _needsReinsertion = false;
-}
-
 void OtherAvatar::simulate(float deltaTime, bool inView) {
     PROFILE_RANGE(simulation, "simulate");
 
diff --git a/interface/src/avatar/OtherAvatar.h b/interface/src/avatar/OtherAvatar.h
index 43bfd2a9ae..498971d6ee 100644
--- a/interface/src/avatar/OtherAvatar.h
+++ b/interface/src/avatar/OtherAvatar.h
@@ -52,9 +52,7 @@ public:
     bool shouldBeInPhysicsSimulation() const;
     bool needsPhysicsUpdate() const;
 
-    btCollisionShape* createCollisionShape(int jointIndex, bool& isBound, std::vector<int>& boundJoints);
-    DetailedMotionState* createMotionState(std::shared_ptr<OtherAvatar> avatar, int jointIndex);
-    void createDetailedMotionStates(const std::shared_ptr<OtherAvatar>& avatar);
+    const btCollisionShape* createCollisionShape(int32_t jointIndex, bool& isBound, std::vector<int32_t>& boundJoints);
     std::vector<DetailedMotionState*>& getDetailedMotionStates() { return _detailedMotionStates; }
     void resetDetailedMotionStates();
     BodyLOD getBodyLOD() { return _bodyLOD; }
diff --git a/interface/src/octree/SafeLanding.cpp b/interface/src/octree/SafeLanding.cpp
index e56ca984e0..479c2a5860 100644
--- a/interface/src/octree/SafeLanding.cpp
+++ b/interface/src/octree/SafeLanding.cpp
@@ -168,7 +168,7 @@ bool isEntityPhysicsReady(const EntityItemPointer& entity) {
             bool hasAABox;
             entity->getAABox(hasAABox);
             if (hasAABox && downloadedCollisionTypes.count(modelEntity->getShapeType()) != 0) {
-                return (!entity->shouldBePhysical() || entity->isReadyToComputeShape() || modelEntity->computeShapeFailedToLoad());
+                return (!entity->shouldBePhysical() || entity->isInPhysicsSimulation() || modelEntity->computeShapeFailedToLoad());
             }
         }
     }
diff --git a/libraries/entities-renderer/src/EntityTreeRenderer.cpp b/libraries/entities-renderer/src/EntityTreeRenderer.cpp
index e8ce812285..fbf577755d 100644
--- a/libraries/entities-renderer/src/EntityTreeRenderer.cpp
+++ b/libraries/entities-renderer/src/EntityTreeRenderer.cpp
@@ -481,6 +481,12 @@ void EntityTreeRenderer::updateChangedEntities(const render::ScenePointer& scene
     }
 }
 
+void EntityTreeRenderer::preUpdate() {
+    if (_tree && !_shuttingDown) {
+        _tree->preUpdate();
+    }
+}
+
 void EntityTreeRenderer::update(bool simulate) {
     PROFILE_RANGE(simulation_physics, "ETR::update");
     PerformanceTimer perfTimer("ETRupdate");
diff --git a/libraries/entities-renderer/src/EntityTreeRenderer.h b/libraries/entities-renderer/src/EntityTreeRenderer.h
index f4284078a3..a0243a159a 100644
--- a/libraries/entities-renderer/src/EntityTreeRenderer.h
+++ b/libraries/entities-renderer/src/EntityTreeRenderer.h
@@ -78,6 +78,7 @@ public:
     void setSetPrecisionPickingOperator(std::function<void(unsigned int, bool)> setPrecisionPickingOperator) { _setPrecisionPickingOperator = setPrecisionPickingOperator; }
 
     void shutdown();
+    void preUpdate();
     void update(bool simulate);
 
     EntityTreePointer getTree() { return std::static_pointer_cast<EntityTree>(_tree); }
diff --git a/libraries/entities-renderer/src/RenderableModelEntityItem.cpp b/libraries/entities-renderer/src/RenderableModelEntityItem.cpp
index bfbbe12ea6..7602028e36 100644
--- a/libraries/entities-renderer/src/RenderableModelEntityItem.cpp
+++ b/libraries/entities-renderer/src/RenderableModelEntityItem.cpp
@@ -735,13 +735,15 @@ bool RenderableModelEntityItem::shouldBePhysical() const {
     auto model = getModel();
     // If we have a model, make sure it hasn't failed to download.
     // If it has, we'll report back that we shouldn't be physical so that physics aren't held waiting for us to be ready.
-    if (model && (getShapeType() == SHAPE_TYPE_COMPOUND || getShapeType() == SHAPE_TYPE_SIMPLE_COMPOUND) && model->didCollisionGeometryRequestFail()) {
-        return false;
-    } else if (model && getShapeType() != SHAPE_TYPE_NONE && model->didVisualGeometryRequestFail()) {
-        return false;
-    } else {
-        return ModelEntityItem::shouldBePhysical();
+    ShapeType shapeType = getShapeType();
+    if (model) {
+        if ((shapeType == SHAPE_TYPE_COMPOUND || shapeType == SHAPE_TYPE_SIMPLE_COMPOUND) && model->didCollisionGeometryRequestFail()) {
+            return false;
+        } else if (shapeType != SHAPE_TYPE_NONE && model->didVisualGeometryRequestFail()) {
+            return false;
+        }
     }
+    return !isDead() && shapeType != SHAPE_TYPE_NONE && QUrl(_modelURL).isValid();
 }
 
 int RenderableModelEntityItem::getJointParent(int index) const {
diff --git a/libraries/entities-renderer/src/RenderablePolyVoxEntityItem.h b/libraries/entities-renderer/src/RenderablePolyVoxEntityItem.h
index 7aea87535e..cca34767a4 100644
--- a/libraries/entities-renderer/src/RenderablePolyVoxEntityItem.h
+++ b/libraries/entities-renderer/src/RenderablePolyVoxEntityItem.h
@@ -72,7 +72,6 @@ public:
     glm::mat4 localToVoxelMatrix() const;
 
     virtual ShapeType getShapeType() const override;
-    virtual bool shouldBePhysical() const override { return !isDead(); }
     virtual bool isReadyToComputeShape() const override;
     virtual void computeShapeInfo(ShapeInfo& info) override;
 
diff --git a/libraries/entities/src/EntityItem.cpp b/libraries/entities/src/EntityItem.cpp
index 7cc35f8be0..d91c11e726 100644
--- a/libraries/entities/src/EntityItem.cpp
+++ b/libraries/entities/src/EntityItem.cpp
@@ -1828,42 +1828,42 @@ void EntityItem::setParentID(const QUuid& value) {
         if (!value.isNull() && tree) {
             EntityItemPointer entity = tree->findEntityByEntityItemID(value);
             if (entity) {
-                newParentNoBootstrapping = entity->getSpecialFlags() & Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING;
+                newParentNoBootstrapping = entity->getSpecialFlags() & Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING;
             }
         }
 
         if (!oldParentID.isNull() && tree) {
             EntityItemPointer entity = tree->findEntityByEntityItemID(oldParentID);
             if (entity) {
-                oldParentNoBootstrapping = entity->getDirtyFlags() & Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING;
+                oldParentNoBootstrapping = entity->getDirtyFlags() & Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING;
             }
         }
 
         if (!value.isNull() && (value == Physics::getSessionUUID() || value == AVATAR_SELF_ID)) {
-            newParentNoBootstrapping |= Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING;
+            newParentNoBootstrapping |= Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING;
         }
 
         if (!oldParentID.isNull() && (oldParentID == Physics::getSessionUUID() || oldParentID == AVATAR_SELF_ID)) {
-            oldParentNoBootstrapping |= Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING;
+            oldParentNoBootstrapping |= Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING;
         }
 
         if ((bool)(oldParentNoBootstrapping ^ newParentNoBootstrapping)) {
-            if ((bool)(newParentNoBootstrapping & Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING)) {
-                markSpecialFlags(Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING);
+            if ((bool)(newParentNoBootstrapping & Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING)) {
+                markSpecialFlags(Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING);
                 forEachDescendant([&](SpatiallyNestablePointer object) {
                         if (object->getNestableType() == NestableType::Entity) {
                             EntityItemPointer entity = std::static_pointer_cast<EntityItem>(object);
                             entity->markDirtyFlags(Simulation::DIRTY_COLLISION_GROUP);
-                            entity->markSpecialFlags(Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING);
+                            entity->markSpecialFlags(Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING);
                         }
                 });
             } else {
-                clearSpecialFlags(Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING);
+                clearSpecialFlags(Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING);
                 forEachDescendant([&](SpatiallyNestablePointer object) {
                         if (object->getNestableType() == NestableType::Entity) {
                             EntityItemPointer entity = std::static_pointer_cast<EntityItem>(object);
                             entity->markDirtyFlags(Simulation::DIRTY_COLLISION_GROUP);
-                            entity->clearSpecialFlags(Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING);
+                            entity->clearSpecialFlags(Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING);
                         }
                 });
             }
@@ -2102,7 +2102,7 @@ void EntityItem::computeCollisionGroupAndFinalMask(int32_t& group, int32_t& mask
             }
         }
 
-        if ((bool)(_flags & Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING)) {
+        if ((bool)(_flags & Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING)) {
             userMask &= ~USER_COLLISION_GROUP_MY_AVATAR;
         }
         mask = Physics::getDefaultCollisionMask(group) & (int32_t)(userMask);
@@ -2173,8 +2173,8 @@ bool EntityItem::addAction(EntitySimulationPointer simulation, EntityDynamicPoin
 }
 
 void EntityItem::enableNoBootstrap() {
-    if (!(bool)(_flags & Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING)) {
-        _flags |= Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING;
+    if (!(bool)(_flags & Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING)) {
+        _flags |= Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING;
         _flags |= Simulation::DIRTY_COLLISION_GROUP; // may need to not collide with own avatar
 
         // NOTE: unlike disableNoBootstrap() below, we do not call simulation->changeEntity() here
@@ -2186,7 +2186,7 @@ void EntityItem::enableNoBootstrap() {
             if (child->getNestableType() == NestableType::Entity) {
                 EntityItemPointer entity = std::static_pointer_cast<EntityItem>(child);
                 entity->markDirtyFlags(Simulation::DIRTY_COLLISION_GROUP);
-                entity->markSpecialFlags(Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING);
+                entity->markSpecialFlags(Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING);
             }
         });
     }
@@ -2194,7 +2194,7 @@ void EntityItem::enableNoBootstrap() {
 
 void EntityItem::disableNoBootstrap() {
     if (!stillHasMyGrabAction()) {
-        _flags &= ~Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING;
+        _flags &= ~Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING;
         _flags |= Simulation::DIRTY_COLLISION_GROUP; // may need to not collide with own avatar
 
         EntityTreePointer entityTree = getTree();
@@ -2207,7 +2207,7 @@ void EntityItem::disableNoBootstrap() {
             if (child->getNestableType() == NestableType::Entity) {
                 EntityItemPointer entity = std::static_pointer_cast<EntityItem>(child);
                 entity->markDirtyFlags(Simulation::DIRTY_COLLISION_GROUP);
-                entity->clearSpecialFlags(Simulation::SPECIAL_FLAGS_NO_BOOTSTRAPPING);
+                entity->clearSpecialFlags(Simulation::SPECIAL_FLAG_NO_BOOTSTRAPPING);
                 simulation->changeEntity(entity);
             }
         });
@@ -2326,7 +2326,7 @@ bool EntityItem::removeActionInternal(const QUuid& actionID, EntitySimulationPoi
         if (removedActionType == DYNAMIC_TYPE_HOLD || removedActionType == DYNAMIC_TYPE_FAR_GRAB) {
             disableNoBootstrap();
         } else {
-            // NO-OP: we assume SPECIAL_FLAGS_NO_BOOTSTRAPPING bits and collision group are correct
+            // NO-OP: we assume SPECIAL_FLAG_NO_BOOTSTRAPPING bits and collision group are correct
             // because they should have been set correctly when the action was added
             // and/or when children were linked
         }
@@ -3154,21 +3154,21 @@ DEFINE_PROPERTY_ACCESSOR(quint32, StaticCertificateVersion, staticCertificateVer
 uint32_t EntityItem::getDirtyFlags() const {
     uint32_t result;
     withReadLock([&] {
-        result = _flags & Simulation::DIRTY_FLAGS;
+        result = _flags & Simulation::DIRTY_FLAGS_MASK;
     });
     return result;
 }
 
 void EntityItem::markDirtyFlags(uint32_t mask) {
     withWriteLock([&] {
-        mask &= Simulation::DIRTY_FLAGS;
+        mask &= Simulation::DIRTY_FLAGS_MASK;
         _flags |= mask;
     });
 }
 
 void EntityItem::clearDirtyFlags(uint32_t mask) {
     withWriteLock([&] {
-        mask &= Simulation::DIRTY_FLAGS;
+        mask &= Simulation::DIRTY_FLAGS_MASK;
         _flags &= ~mask;
     });
 }
@@ -3176,21 +3176,21 @@ void EntityItem::clearDirtyFlags(uint32_t mask) {
 uint32_t EntityItem::getSpecialFlags() const {
     uint32_t result;
     withReadLock([&] {
-        result = _flags & Simulation::SPECIAL_FLAGS;
+        result = _flags & Simulation::SPECIAL_FLAGS_MASK;
     });
     return result;
 }
 
 void EntityItem::markSpecialFlags(uint32_t mask) {
     withWriteLock([&] {
-        mask &= Simulation::SPECIAL_FLAGS;
+        mask &= Simulation::SPECIAL_FLAGS_MASK;
         _flags |= mask;
     });
 }
 
 void EntityItem::clearSpecialFlags(uint32_t mask) {
     withWriteLock([&] {
-        mask &= Simulation::SPECIAL_FLAGS;
+        mask &= Simulation::SPECIAL_FLAGS_MASK;
         _flags &= ~mask;
     });
 }
diff --git a/libraries/entities/src/EntityItem.h b/libraries/entities/src/EntityItem.h
index 29a1a8d73c..ea4b11e0b0 100644
--- a/libraries/entities/src/EntityItem.h
+++ b/libraries/entities/src/EntityItem.h
@@ -23,6 +23,7 @@
 #include <OctreeElement.h> // for OctreeElement::AppendState
 #include <OctreePacketData.h>
 #include <PhysicsCollisionGroups.h>
+#include <SimulationFlags.h>
 #include <ShapeInfo.h>
 #include <Transform.h>
 #include <SpatiallyNestable.h>
@@ -33,11 +34,11 @@
 #include "EntityPropertyFlags.h"
 #include "EntityTypes.h"
 #include "SimulationOwner.h"
-#include "SimulationFlags.h"
 #include "EntityDynamicInterface.h"
 #include "GrabPropertyGroup.h"
 
 class EntitySimulation;
+using EntitySimulationPointer = std::shared_ptr<EntitySimulation>;
 class EntityTreeElement;
 class EntityTreeElementExtraEncodeData;
 class EntityDynamicInterface;
@@ -322,7 +323,7 @@ public:
     bool getDynamic() const;
     void setDynamic(bool value);
 
-    virtual bool shouldBePhysical() const { return false; }
+    virtual bool shouldBePhysical() const { return !isDead() && getShapeType() != SHAPE_TYPE_NONE; }
     bool isVisuallyReady() const { return _visuallyReady; }
 
     bool getLocked() const;
@@ -423,8 +424,9 @@ public:
 
     bool isSimulated() const { return _simulated; }
 
-    void* getPhysicsInfo() const { return _physicsInfo; }
+    bool isInPhysicsSimulation() const { return (bool)(_flags & Simulation::SPECIAL_FLAG_IN_PHYSICS_SIMULATION); }
 
+    void* getPhysicsInfo() const { return _physicsInfo; }
     void setPhysicsInfo(void* data) { _physicsInfo = data; }
 
     EntityTreeElementPointer getElement() const { return _element; }
diff --git a/libraries/entities/src/EntitySimulation.cpp b/libraries/entities/src/EntitySimulation.cpp
index 05e71a8f06..b5e4fed0fd 100644
--- a/libraries/entities/src/EntitySimulation.cpp
+++ b/libraries/entities/src/EntitySimulation.cpp
@@ -176,47 +176,44 @@ void EntitySimulation::addEntity(EntityItemPointer entity) {
 void EntitySimulation::changeEntity(EntityItemPointer entity) {
     QMutexLocker lock(&_mutex);
     assert(entity);
-    if (!entity->isSimulated()) {
-        // This entity was either never added to the simulation or has been removed
-        // (probably for pending delete), so we don't want to keep a pointer to it
-        // on any internal lists.
-        return;
-    }
+    _changedEntities.insert(entity);
+}
 
-    // Although it is not the responsibility of the EntitySimulation to sort the tree for EXTERNAL changes
-    // it IS responsibile for triggering deletes for entities that leave the bounds of the domain, hence
-    // we must check for that case here, however we rely on the change event to have set DIRTY_POSITION flag.
+void EntitySimulation::processChangedEntities() {
+    QMutexLocker lock(&_mutex);
+    PROFILE_RANGE_EX(simulation_physics, "processChangedEntities", 0xffff00ff, (uint64_t)_changedEntities.size());
+    for (auto& entity : _changedEntities) {
+        if (entity->isSimulated()) {
+            processChangedEntity(entity);
+        }
+    }
+    _changedEntities.clear();
+}
+
+void EntitySimulation::processChangedEntity(const EntityItemPointer& entity) {
     uint32_t dirtyFlags = entity->getDirtyFlags();
-    if (dirtyFlags & Simulation::DIRTY_POSITION) {
-        AACube domainBounds(glm::vec3((float)-HALF_TREE_SCALE), (float)TREE_SCALE);
-        bool success;
-        AACube newCube = entity->getQueryAACube(success);
-        if (success && !domainBounds.touches(newCube)) {
-            qCDebug(entities) << "Entity " << entity->getEntityItemID() << " moved out of domain bounds.";
-            entity->die();
-            prepareEntityForDelete(entity);
-            return;
-        }
-    }
 
-    if (dirtyFlags & Simulation::DIRTY_LIFETIME) {
-        if (entity->isMortal()) {
-            _mortalEntities.insert(entity);
-            uint64_t expiry = entity->getExpiry();
-            if (expiry < _nextExpiry) {
-                _nextExpiry = expiry;
+    if (dirtyFlags & (Simulation::DIRTY_LIFETIME | Simulation::DIRTY_UPDATEABLE)) {
+        if (dirtyFlags & Simulation::DIRTY_LIFETIME) {
+            if (entity->isMortal()) {
+                _mortalEntities.insert(entity);
+                uint64_t expiry = entity->getExpiry();
+                if (expiry < _nextExpiry) {
+                    _nextExpiry = expiry;
+                }
+            } else {
+                _mortalEntities.remove(entity);
             }
-        } else {
-            _mortalEntities.remove(entity);
         }
-        entity->clearDirtyFlags(Simulation::DIRTY_LIFETIME);
+        if (dirtyFlags & Simulation::DIRTY_UPDATEABLE) {
+            if (entity->needsToCallUpdate()) {
+                _entitiesToUpdate.insert(entity);
+            } else {
+                _entitiesToUpdate.remove(entity);
+            }
+        }
+        entity->clearDirtyFlags(Simulation::DIRTY_LIFETIME | Simulation::DIRTY_UPDATEABLE);
     }
-    if (entity->needsToCallUpdate()) {
-        _entitiesToUpdate.insert(entity);
-    } else {
-        _entitiesToUpdate.remove(entity);
-    }
-    changeEntityInternal(entity);
 }
 
 void EntitySimulation::clearEntities() {
diff --git a/libraries/entities/src/EntitySimulation.h b/libraries/entities/src/EntitySimulation.h
index f107bcae6e..1dd0369561 100644
--- a/libraries/entities/src/EntitySimulation.h
+++ b/libraries/entities/src/EntitySimulation.h
@@ -13,6 +13,7 @@
 #define hifi_EntitySimulation_h
 
 #include <limits>
+#include <unordered_set>
 
 #include <QtCore/QObject>
 #include <QSet>
@@ -82,13 +83,15 @@ public:
     /// \param entity pointer to EntityItem that needs to be put on the entitiesToDelete list and removed from others.
     virtual void prepareEntityForDelete(EntityItemPointer entity);
 
+    void processChangedEntities();
+
 protected:
     // These pure virtual methods are protected because they are not to be called will-nilly. The base class
     // calls them in the right places.
     virtual void updateEntitiesInternal(uint64_t now) = 0;
     virtual void addEntityInternal(EntityItemPointer entity) = 0;
     virtual void removeEntityInternal(EntityItemPointer entity);
-    virtual void changeEntityInternal(EntityItemPointer entity) = 0;
+    virtual void processChangedEntity(const EntityItemPointer& entity);
     virtual void clearEntitiesInternal() = 0;
 
     void expireMortalEntities(uint64_t now);
@@ -114,11 +117,11 @@ private:
 
     // We maintain multiple lists, each for its distinct purpose.
     // An entity may be in more than one list.
+    std::unordered_set<EntityItemPointer> _changedEntities; // all changes this frame
     SetOfEntities _allEntities; // tracks all entities added the simulation
     SetOfEntities _mortalEntities; // entities that have an expiry
     uint64_t _nextExpiry;
 
-
     SetOfEntities _entitiesToUpdate; // entities that need to call EntityItem::update()
 };
 
diff --git a/libraries/entities/src/EntityTree.cpp b/libraries/entities/src/EntityTree.cpp
index b3dd78ae92..fe8c8c9336 100644
--- a/libraries/entities/src/EntityTree.cpp
+++ b/libraries/entities/src/EntityTree.cpp
@@ -2079,7 +2079,6 @@ void EntityTree::entityChanged(EntityItemPointer entity) {
 }
 
 void EntityTree::fixupNeedsParentFixups() {
-    PROFILE_RANGE(simulation_physics, "FixupParents");
     MovingEntitiesOperator moveOperator;
     QVector<EntityItemWeakPointer> entitiesToFixup;
     {
@@ -2189,11 +2188,19 @@ void EntityTree::addToNeedsParentFixupList(EntityItemPointer entity) {
     _needsParentFixup.append(entity);
 }
 
+void EntityTree::preUpdate() {
+    withWriteLock([&] {
+        fixupNeedsParentFixups();
+        if (_simulation) {
+            _simulation->processChangedEntities();
+        }
+    });
+}
+
 void EntityTree::update(bool simulate) {
     PROFILE_RANGE(simulation_physics, "UpdateTree");
     PerformanceTimer perfTimer("updateTree");
     withWriteLock([&] {
-        fixupNeedsParentFixups();
         if (simulate && _simulation) {
             _simulation->updateEntities();
             {
diff --git a/libraries/entities/src/EntityTree.h b/libraries/entities/src/EntityTree.h
index c80517c82b..9108f8d8d2 100644
--- a/libraries/entities/src/EntityTree.h
+++ b/libraries/entities/src/EntityTree.h
@@ -109,9 +109,10 @@ public:
 
     virtual void releaseSceneEncodeData(OctreeElementExtraEncodeData* extraEncodeData) const override;
 
-    virtual void update() override { update(true); }
-
-    void update(bool simulate);
+    // Why preUpdate() and update()?
+    // Because sometimes we need to do stuff between the two.
+    void preUpdate() override;
+    void update(bool simulate = true) override;
 
     // The newer API...
     void postAddEntity(EntityItemPointer entityItem);
diff --git a/libraries/entities/src/ModelEntityItem.cpp b/libraries/entities/src/ModelEntityItem.cpp
index 505ee26c0f..cb9637acd5 100644
--- a/libraries/entities/src/ModelEntityItem.cpp
+++ b/libraries/entities/src/ModelEntityItem.cpp
@@ -421,11 +421,6 @@ void ModelEntityItem::setAnimationFPS(float value) {
     });
 }
 
-// virtual
-bool ModelEntityItem::shouldBePhysical() const {
-    return !isDead() && getShapeType() != SHAPE_TYPE_NONE && QUrl(_modelURL).isValid();
-}
-
 void ModelEntityItem::resizeJointArrays(int newSize) {
     if (newSize < 0) {
         return;
diff --git a/libraries/entities/src/ModelEntityItem.h b/libraries/entities/src/ModelEntityItem.h
index d532fefe7e..75a695f1c0 100644
--- a/libraries/entities/src/ModelEntityItem.h
+++ b/libraries/entities/src/ModelEntityItem.h
@@ -118,8 +118,6 @@ public:
     const QString getTextures() const;
     void setTextures(const QString& textures);
 
-    virtual bool shouldBePhysical() const override;
-
     virtual void setJointRotations(const QVector<glm::quat>& rotations);
     virtual void setJointRotationsSet(const QVector<bool>& rotationsSet);
     virtual void setJointTranslations(const QVector<glm::vec3>& translations);
diff --git a/libraries/entities/src/ParticleEffectEntityItem.h b/libraries/entities/src/ParticleEffectEntityItem.h
index 52f229201e..b526298a4b 100644
--- a/libraries/entities/src/ParticleEffectEntityItem.h
+++ b/libraries/entities/src/ParticleEffectEntityItem.h
@@ -231,6 +231,8 @@ public:
                                                  EntityPropertyFlags& propertyFlags, bool overwriteLocalData,
                                                  bool& somethingChanged) override;
 
+    bool shouldBePhysical() const override { return false; }
+
     void setColor(const glm::u8vec3& value);
     glm::u8vec3 getColor() const { return _particleProperties.color.gradient.target; }
 
diff --git a/libraries/entities/src/PolyVoxEntityItem.h b/libraries/entities/src/PolyVoxEntityItem.h
index dd05ce67b1..a6076dfda7 100644
--- a/libraries/entities/src/PolyVoxEntityItem.h
+++ b/libraries/entities/src/PolyVoxEntityItem.h
@@ -164,7 +164,6 @@ class PolyVoxEntityItem : public EntityItem {
     glm::vec3 getSurfacePositionAdjustment() const;
 
     virtual ShapeType getShapeType() const override;
-    virtual bool shouldBePhysical() const override { return !isDead(); }
 
     bool isEdged() const;
 
diff --git a/libraries/entities/src/ShapeEntityItem.h b/libraries/entities/src/ShapeEntityItem.h
index fc590e06a4..3622c74f50 100644
--- a/libraries/entities/src/ShapeEntityItem.h
+++ b/libraries/entities/src/ShapeEntityItem.h
@@ -84,8 +84,6 @@ public:
 
     void setUnscaledDimensions(const glm::vec3& value) override;
 
-    bool shouldBePhysical() const override { return !isDead(); }
-
     bool supportsDetailedIntersection() const override;
     bool findDetailedRayIntersection(const glm::vec3& origin, const glm::vec3& direction,
                                                 OctreeElementPointer& element, float& distance,
diff --git a/libraries/entities/src/SimpleEntitySimulation.cpp b/libraries/entities/src/SimpleEntitySimulation.cpp
index 28dc7b26c4..b8e3df2d03 100644
--- a/libraries/entities/src/SimpleEntitySimulation.cpp
+++ b/libraries/entities/src/SimpleEntitySimulation.cpp
@@ -85,7 +85,9 @@ void SimpleEntitySimulation::removeEntityInternal(EntityItemPointer entity) {
     _entitiesThatNeedSimulationOwner.remove(entity);
 }
 
-void SimpleEntitySimulation::changeEntityInternal(EntityItemPointer entity) {
+void SimpleEntitySimulation::processChangedEntity(const EntityItemPointer& entity) {
+    EntitySimulation::processChangedEntity(entity);
+
     uint32_t flags = entity->getDirtyFlags();
     if ((flags & Simulation::DIRTY_SIMULATOR_ID) || (flags & Simulation::DIRTY_VELOCITIES)) {
         if (entity->getSimulatorID().isNull()) {
diff --git a/libraries/entities/src/SimpleEntitySimulation.h b/libraries/entities/src/SimpleEntitySimulation.h
index 8ac9b69e93..1b240a8bf0 100644
--- a/libraries/entities/src/SimpleEntitySimulation.h
+++ b/libraries/entities/src/SimpleEntitySimulation.h
@@ -31,7 +31,7 @@ protected:
     void updateEntitiesInternal(uint64_t now) override;
     void addEntityInternal(EntityItemPointer entity) override;
     void removeEntityInternal(EntityItemPointer entity) override;
-    void changeEntityInternal(EntityItemPointer entity) override;
+    void processChangedEntity(const EntityItemPointer& entity) override;
     void clearEntitiesInternal() override;
 
     void sortEntitiesThatMoved() override;
diff --git a/libraries/entities/src/SimulationOwner.h b/libraries/entities/src/SimulationOwner.h
index f574234354..6f37066e47 100644
--- a/libraries/entities/src/SimulationOwner.h
+++ b/libraries/entities/src/SimulationOwner.h
@@ -89,6 +89,8 @@
 //    (14) When an entity's ownership priority drops to YIELD (=1, below VOLUNTEER) other participants may
 //         bid for it immediately at VOLUNTEER.
 //
+/* These declarations temporarily moved to SimulationFlags.h while we unravel some spaghetti dependencies.
+ * The intent is to move them back here once the dust settles.
 const uint8_t YIELD_SIMULATION_PRIORITY = 1;
 const uint8_t VOLUNTEER_SIMULATION_PRIORITY = YIELD_SIMULATION_PRIORITY + 1;
 const uint8_t RECRUIT_SIMULATION_PRIORITY = VOLUNTEER_SIMULATION_PRIORITY + 1;
@@ -101,6 +103,7 @@ const uint8_t SCRIPT_POKE_SIMULATION_PRIORITY = SCRIPT_GRAB_SIMULATION_PRIORITY
 // which really just means: things that collide with it will be bid at a priority level one lower
 const uint8_t PERSONAL_SIMULATION_PRIORITY = SCRIPT_GRAB_SIMULATION_PRIORITY;
 const uint8_t AVATAR_ENTITY_SIMULATION_PRIORITY = PERSONAL_SIMULATION_PRIORITY;
+*/
 
 
 class SimulationOwner {
diff --git a/libraries/entities/src/ZoneEntityItem.h b/libraries/entities/src/ZoneEntityItem.h
index 69e3227135..34ad47f095 100644
--- a/libraries/entities/src/ZoneEntityItem.h
+++ b/libraries/entities/src/ZoneEntityItem.h
@@ -62,6 +62,7 @@ public:
     virtual bool isReadyToComputeShape() const override { return false; }
     virtual void setShapeType(ShapeType type) override;
     virtual ShapeType getShapeType() const override;
+    bool shouldBePhysical() const override { return false; }
 
     QString getCompoundShapeURL() const;
     virtual void setCompoundShapeURL(const QString& url);
diff --git a/libraries/octree/src/Octree.h b/libraries/octree/src/Octree.h
index 82076f618b..4f994da60e 100644
--- a/libraries/octree/src/Octree.h
+++ b/libraries/octree/src/Octree.h
@@ -145,7 +145,10 @@ public:
     virtual bool rootElementHasData() const { return false; }
     virtual void releaseSceneEncodeData(OctreeElementExtraEncodeData* extraEncodeData) const { }
 
-    virtual void update() { } // nothing to do by default
+    // Why preUpdate() and update()?
+    // Because EntityTree needs them.
+    virtual void preUpdate() { }
+    virtual void update(bool simulate = true) { }
 
     OctreeElementPointer getRoot() { return _rootElement; }
 
diff --git a/libraries/octree/src/OctreePersistThread.cpp b/libraries/octree/src/OctreePersistThread.cpp
index 20ba3cde60..dd2cc12d50 100644
--- a/libraries/octree/src/OctreePersistThread.cpp
+++ b/libraries/octree/src/OctreePersistThread.cpp
@@ -242,6 +242,7 @@ bool OctreePersistThread::backupCurrentFile() {
 }
 
 void OctreePersistThread::process() {
+    _tree->preUpdate();
     _tree->update();
 
     auto now = std::chrono::steady_clock::now();
diff --git a/libraries/physics/src/EntityMotionState.cpp b/libraries/physics/src/EntityMotionState.cpp
index 6abe5c3899..67aa7d2d7d 100644
--- a/libraries/physics/src/EntityMotionState.cpp
+++ b/libraries/physics/src/EntityMotionState.cpp
@@ -25,23 +25,6 @@
 #include "PhysicsHelpers.h"
 #include "PhysicsLogging.h"
 
-#ifdef WANT_DEBUG_ENTITY_TREE_LOCKS
-#include "EntityTree.h"
-
-bool EntityMotionState::entityTreeIsLocked() const {
-    EntityTreeElementPointer element = _entity->getElement();
-    EntityTreePointer tree = element ? element->getTree() : nullptr;
-    if (!tree) {
-        return true;
-    }
-    return true;
-}
-#else
-bool entityTreeIsLocked() {
-    return true;
-}
-#endif
-
 const uint8_t LOOPS_FOR_SIMULATION_ORPHAN = 50;
 const quint64 USECS_BETWEEN_OWNERSHIP_BIDS = USECS_PER_SECOND / 5;
 
@@ -74,7 +57,6 @@ EntityMotionState::EntityMotionState(btCollisionShape* shape, EntityItemPointer
 
     _type = MOTIONSTATE_TYPE_ENTITY;
     assert(_entity);
-    assert(entityTreeIsLocked());
     setMass(_entity->computeMass());
     // we need the side-effects of EntityMotionState::setShape() so we call it explicitly here
     // rather than pass the legit shape pointer to the ObjectMotionState ctor above.
@@ -143,7 +125,6 @@ void EntityMotionState::handleDeactivation() {
 
 // virtual
 void EntityMotionState::handleEasyChanges(uint32_t& flags) {
-    assert(entityTreeIsLocked());
     updateServerPhysicsVariables();
     ObjectMotionState::handleEasyChanges(flags);
 
@@ -191,17 +172,10 @@ void EntityMotionState::handleEasyChanges(uint32_t& flags) {
 }
 
 
-// virtual
-bool EntityMotionState::handleHardAndEasyChanges(uint32_t& flags, PhysicsEngine* engine) {
-    updateServerPhysicsVariables();
-    return ObjectMotionState::handleHardAndEasyChanges(flags, engine);
-}
-
 PhysicsMotionType EntityMotionState::computePhysicsMotionType() const {
     if (!_entity) {
         return MOTION_TYPE_STATIC;
     }
-    assert(entityTreeIsLocked());
 
     if (_entity->getLocked()) {
         if (_entity->isMoving()) {
@@ -226,7 +200,6 @@ PhysicsMotionType EntityMotionState::computePhysicsMotionType() const {
 }
 
 bool EntityMotionState::isMoving() const {
-    assert(entityTreeIsLocked());
     return _entity && _entity->isMovingRelativeToParent();
 }
 
@@ -240,7 +213,6 @@ void EntityMotionState::getWorldTransform(btTransform& worldTrans) const {
     if (!_entity) {
         return;
     }
-    assert(entityTreeIsLocked());
     if (_motionType == MOTION_TYPE_KINEMATIC) {
         BT_PROFILE("kinematicIntegration");
         uint32_t thisStep = ObjectMotionState::getWorldSimulationStep();
@@ -271,7 +243,6 @@ void EntityMotionState::getWorldTransform(btTransform& worldTrans) const {
 // This callback is invoked by the physics simulation at the end of each simulation step...
 // iff the corresponding RigidBody is DYNAMIC and ACTIVE.
 void EntityMotionState::setWorldTransform(const btTransform& worldTrans) {
-    assert(entityTreeIsLocked());
     measureBodyAcceleration();
 
     // If transform or velocities are flagged as dirty it means a network or scripted change
@@ -309,19 +280,6 @@ void EntityMotionState::setWorldTransform(const btTransform& worldTrans) {
 }
 
 
-// virtual and protected
-bool EntityMotionState::isReadyToComputeShape() const {
-    return _entity->isReadyToComputeShape();
-}
-
-// virtual and protected
-const btCollisionShape* EntityMotionState::computeNewShape() {
-    ShapeInfo shapeInfo;
-    assert(entityTreeIsLocked());
-    _entity->computeShapeInfo(shapeInfo);
-    return getShapeManager()->getShape(shapeInfo);
-}
-
 const uint8_t MAX_NUM_INACTIVE_UPDATES = 20;
 
 bool EntityMotionState::remoteSimulationOutOfSync(uint32_t simulationStep) {
@@ -439,7 +397,6 @@ bool EntityMotionState::shouldSendUpdate(uint32_t simulationStep) {
     DETAILED_PROFILE_RANGE(simulation_physics, "ShouldSend");
     // NOTE: we expect _entity and _body to be valid in this context, since shouldSendUpdate() is only called
     // after doesNotNeedToSendUpdate() returns false and that call should return 'true' if _entity or _body are NULL.
-    assert(entityTreeIsLocked());
 
     // this case is prevented by setting _ownershipState to UNOWNABLE in EntityMotionState::ctor
     assert(!(_entity->isAvatarEntity() && _entity->getOwningAvatarID() != Physics::getSessionUUID()));
@@ -505,7 +462,6 @@ void EntityMotionState::updateSendVelocities() {
 
 void EntityMotionState::sendBid(OctreeEditPacketSender* packetSender, uint32_t step) {
     DETAILED_PROFILE_RANGE(simulation_physics, "Bid");
-    assert(entityTreeIsLocked());
 
     updateSendVelocities();
 
@@ -546,7 +502,6 @@ void EntityMotionState::sendBid(OctreeEditPacketSender* packetSender, uint32_t s
 
 void EntityMotionState::sendUpdate(OctreeEditPacketSender* packetSender, uint32_t step) {
     DETAILED_PROFILE_RANGE(simulation_physics, "Send");
-    assert(entityTreeIsLocked());
     assert(isLocallyOwned());
 
     updateSendVelocities();
@@ -645,8 +600,7 @@ void EntityMotionState::sendUpdate(OctreeEditPacketSender* packetSender, uint32_
     _bumpedPriority = 0;
 }
 
-uint32_t EntityMotionState::getIncomingDirtyFlags() {
-    assert(entityTreeIsLocked());
+uint32_t EntityMotionState::getIncomingDirtyFlags() const {
     uint32_t dirtyFlags = 0;
     if (_body && _entity) {
         dirtyFlags = _entity->getDirtyFlags();
@@ -676,10 +630,9 @@ uint32_t EntityMotionState::getIncomingDirtyFlags() {
     return dirtyFlags;
 }
 
-void EntityMotionState::clearIncomingDirtyFlags() {
-    assert(entityTreeIsLocked());
+void EntityMotionState::clearIncomingDirtyFlags(uint32_t mask) {
     if (_body && _entity) {
-        _entity->clearDirtyFlags(DIRTY_PHYSICS_FLAGS);
+        _entity->clearDirtyFlags(mask);
     }
 }
 
@@ -694,7 +647,6 @@ void EntityMotionState::slaveBidPriority() {
 
 // virtual
 QUuid EntityMotionState::getSimulatorID() const {
-    assert(entityTreeIsLocked());
     return _entity->getSimulatorID();
 }
 
@@ -762,6 +714,10 @@ glm::vec3 EntityMotionState::getObjectLinearVelocityChange() const {
     return _measuredAcceleration * _measuredDeltaTime;
 }
 
+bool EntityMotionState::shouldBeInPhysicsSimulation() const {
+    return _region < workload::Region::R3 && _entity->shouldBePhysical();
+}
+
 // virtual
 void EntityMotionState::setMotionType(PhysicsMotionType motionType) {
     ObjectMotionState::setMotionType(motionType);
@@ -770,7 +726,6 @@ void EntityMotionState::setMotionType(PhysicsMotionType motionType) {
 
 // virtual
 QString EntityMotionState::getName() const {
-    assert(entityTreeIsLocked());
     return _entity->getName();
 }
 
@@ -788,6 +743,15 @@ bool EntityMotionState::shouldSendBid() const {
         && !_entity->getLocked();
 }
 
+void EntityMotionState::setRigidBody(btRigidBody* body) {
+    ObjectMotionState::setRigidBody(body);
+    if (_body) {
+        _entity->markSpecialFlags(Simulation::SPECIAL_FLAG_IN_PHYSICS_SIMULATION);
+    } else {
+        _entity->clearSpecialFlags(Simulation::SPECIAL_FLAG_IN_PHYSICS_SIMULATION);
+    }
+}
+
 uint8_t EntityMotionState::computeFinalBidPriority() const {
     return (_region == workload::Region::R1) ?
         glm::max(glm::max(VOLUNTEER_SIMULATION_PRIORITY, _bumpedPriority), _entity->getScriptSimulationPriority()) : 0;
diff --git a/libraries/physics/src/EntityMotionState.h b/libraries/physics/src/EntityMotionState.h
index ddf384dc77..7456837777 100644
--- a/libraries/physics/src/EntityMotionState.h
+++ b/libraries/physics/src/EntityMotionState.h
@@ -12,6 +12,7 @@
 #ifndef hifi_EntityMotionState_h
 #define hifi_EntityMotionState_h
 
+#include <EntityItem.h>
 #include <EntityTypes.h>
 #include <AACube.h>
 #include <workload/Region.h>
@@ -38,7 +39,6 @@ public:
 
     void handleDeactivation();
     virtual void handleEasyChanges(uint32_t& flags) override;
-    virtual bool handleHardAndEasyChanges(uint32_t& flags, PhysicsEngine* engine) override;
 
     /// \return PhysicsMotionType based on params set in EntityItem
     virtual PhysicsMotionType computePhysicsMotionType() const override;
@@ -55,8 +55,8 @@ public:
     void sendBid(OctreeEditPacketSender* packetSender, uint32_t step);
     void sendUpdate(OctreeEditPacketSender* packetSender, uint32_t step);
 
-    virtual uint32_t getIncomingDirtyFlags() override;
-    virtual void clearIncomingDirtyFlags() override;
+    virtual uint32_t getIncomingDirtyFlags() const override;
+    virtual void clearIncomingDirtyFlags(uint32_t mask = DIRTY_PHYSICS_FLAGS) override;
 
     virtual float getObjectRestitution() const override { return _entity->getRestitution(); }
     virtual float getObjectFriction() const override { return _entity->getFriction(); }
@@ -84,6 +84,7 @@ public:
     void measureBodyAcceleration();
 
     virtual QString getName() const override;
+    ShapeType getShapeType() const override { return _entity->getShapeType(); }
 
     virtual void computeCollisionGroupAndMask(int32_t& group, int32_t& mask) const override;
 
@@ -99,6 +100,8 @@ public:
     void saveKinematicState(btScalar timeStep) override;
 
 protected:
+    void setRigidBody(btRigidBody* body) override;
+
     uint8_t computeFinalBidPriority() const;
     void updateSendVelocities();
     uint64_t getNextBidExpiry() const { return _nextBidExpiry; }
@@ -112,12 +115,8 @@ protected:
 
     void clearObjectVelocities() const;
 
-    #ifdef WANT_DEBUG_ENTITY_TREE_LOCKS
-    bool entityTreeIsLocked() const;
-    #endif
-
-    bool isReadyToComputeShape() const override;
-    const btCollisionShape* computeNewShape() override;
+    bool isInPhysicsSimulation() const { return _body != nullptr; }
+    bool shouldBeInPhysicsSimulation() const;
     void setMotionType(PhysicsMotionType motionType) override;
 
     // EntityMotionState keeps a SharedPointer to its EntityItem which is only set in the CTOR
diff --git a/libraries/physics/src/ObjectActionTractor.cpp b/libraries/physics/src/ObjectActionTractor.cpp
index c7681e217c..b53c2e137a 100644
--- a/libraries/physics/src/ObjectActionTractor.cpp
+++ b/libraries/physics/src/ObjectActionTractor.cpp
@@ -11,7 +11,8 @@
 
 #include "ObjectActionTractor.h"
 
-#include "QVariantGLM.h"
+#include <EntityItem.h>
+#include <QVariantGLM.h>
 
 #include "PhysicsLogging.h"
 
diff --git a/libraries/physics/src/ObjectActionTravelOriented.cpp b/libraries/physics/src/ObjectActionTravelOriented.cpp
index bd32ed13ff..b27ec40ae4 100644
--- a/libraries/physics/src/ObjectActionTravelOriented.cpp
+++ b/libraries/physics/src/ObjectActionTravelOriented.cpp
@@ -13,7 +13,9 @@
 
 #include <glm/gtc/quaternion.hpp>
 
-#include "QVariantGLM.h"
+#include <EntityItem.h>
+#include <QVariantGLM.h>
+
 #include "PhysicsLogging.h"
 
 const uint16_t ObjectActionTravelOriented::actionVersion = 1;
diff --git a/libraries/physics/src/ObjectDynamic.h b/libraries/physics/src/ObjectDynamic.h
index f41d6cd51d..49fa615b88 100644
--- a/libraries/physics/src/ObjectDynamic.h
+++ b/libraries/physics/src/ObjectDynamic.h
@@ -17,7 +17,9 @@
 
 #include <btBulletDynamicsCommon.h>
 
+#include <EntityItemID.h>
 #include <shared/ReadWriteLockable.h>
+#include <SpatiallyNestable.h>
 
 #include "ObjectMotionState.h"
 #include "BulletUtil.h"
diff --git a/libraries/physics/src/ObjectMotionState.cpp b/libraries/physics/src/ObjectMotionState.cpp
index 0ab051fa96..ad7332cb15 100644
--- a/libraries/physics/src/ObjectMotionState.cpp
+++ b/libraries/physics/src/ObjectMotionState.cpp
@@ -198,9 +198,14 @@ void ObjectMotionState::setShape(const btCollisionShape* shape) {
             getShapeManager()->releaseShape(_shape);
         }
         _shape = shape;
-        if (_body && _type != MOTIONSTATE_TYPE_DETAILED) {
+        if (_body) {
+            assert(_shape);
+            _body->setCollisionShape(const_cast<btCollisionShape*>(_shape));
             updateCCDConfiguration();
         }
+    } else if (shape) {
+        // we need to release unused reference to shape
+        getShapeManager()->releaseShape(shape);
     }
 }
 
@@ -285,50 +290,6 @@ void ObjectMotionState::handleEasyChanges(uint32_t& flags) {
     }
 }
 
-bool ObjectMotionState::handleHardAndEasyChanges(uint32_t& flags, PhysicsEngine* engine) {
-    assert(_body && _shape);
-    if (flags & Simulation::DIRTY_SHAPE) {
-        // make sure the new shape is valid
-        if (!isReadyToComputeShape()) {
-            return false;
-        }
-        const btCollisionShape* newShape = computeNewShape();
-        if (!newShape) {
-            qCDebug(physics) << "Warning: failed to generate new shape!";
-            // failed to generate new shape! --> keep old shape and remove shape-change flag
-            flags &= ~Simulation::DIRTY_SHAPE;
-            // TODO: force this object out of PhysicsEngine rather than just use the old shape
-            if ((flags & HARD_DIRTY_PHYSICS_FLAGS) == 0) {
-                // no HARD flags remain, so do any EASY changes
-                if (flags & EASY_DIRTY_PHYSICS_FLAGS) {
-                    handleEasyChanges(flags);
-                }
-                return true;
-            }
-        } else {
-            if (_shape == newShape) {
-                // the shape didn't actually change, so we clear the DIRTY_SHAPE flag
-                flags &= ~Simulation::DIRTY_SHAPE;
-                // and clear the reference we just created
-                getShapeManager()->releaseShape(_shape);        
-            } else {
-                _body->setCollisionShape(const_cast<btCollisionShape*>(newShape));
-                setShape(newShape);
-            }
-        }
-    }
-    if (flags & EASY_DIRTY_PHYSICS_FLAGS) {
-        handleEasyChanges(flags);
-    }
-    // it is possible there are no HARD flags at this point (if DIRTY_SHAPE was removed)
-    // so we check again before we reinsert:
-    if (flags & HARD_DIRTY_PHYSICS_FLAGS) {
-        engine->reinsertObject(this);
-    }
-
-    return true;
-}
-
 void ObjectMotionState::updateBodyMaterialProperties() {
     _body->setRestitution(getObjectRestitution());
     _body->setFriction(getObjectFriction());
diff --git a/libraries/physics/src/ObjectMotionState.h b/libraries/physics/src/ObjectMotionState.h
index fe175a2c7d..415b388e70 100644
--- a/libraries/physics/src/ObjectMotionState.h
+++ b/libraries/physics/src/ObjectMotionState.h
@@ -18,7 +18,7 @@
 #include <QSet>
 #include <QVector>
 
-#include <EntityItem.h>
+#include <SimulationFlags.h>
 
 #include "ContactInfo.h"
 #include "ShapeManager.h"
@@ -100,7 +100,6 @@ public:
     virtual ~ObjectMotionState();
 
     virtual void handleEasyChanges(uint32_t& flags);
-    virtual bool handleHardAndEasyChanges(uint32_t& flags, PhysicsEngine* engine);
 
     void updateBodyMaterialProperties();
     void updateBodyVelocities();
@@ -123,11 +122,12 @@ public:
     glm::vec3 getBodyAngularVelocity() const;
     virtual glm::vec3 getObjectLinearVelocityChange() const;
 
-    virtual uint32_t getIncomingDirtyFlags() = 0;
-    virtual void clearIncomingDirtyFlags() = 0;
+    virtual uint32_t getIncomingDirtyFlags() const = 0;
+    virtual void clearIncomingDirtyFlags(uint32_t mask = DIRTY_PHYSICS_FLAGS) = 0;
 
     virtual PhysicsMotionType computePhysicsMotionType() const = 0;
 
+    virtual bool needsNewShape() const { return _shape == nullptr || getIncomingDirtyFlags() & Simulation::DIRTY_SHAPE; }
     const btCollisionShape* getShape() const { return _shape; }
     btRigidBody* getRigidBody() const { return _body; }
 
@@ -154,6 +154,7 @@ public:
     virtual void bump(uint8_t priority) {}
 
     virtual QString getName() const { return ""; }
+    virtual ShapeType getShapeType() const = 0;
 
     virtual void computeCollisionGroupAndMask(int32_t& group, int32_t& mask) const = 0;
 
@@ -172,8 +173,6 @@ public:
     friend class PhysicsEngine;
 
 protected:
-    virtual bool isReadyToComputeShape() const = 0;
-    virtual const btCollisionShape* computeNewShape() = 0;
     virtual void setMotionType(PhysicsMotionType motionType);
     void updateCCDConfiguration();
 
@@ -187,7 +186,7 @@ protected:
     btRigidBody* _body { nullptr };
     float _density { 1.0f };
 
-    // ACTION_CAN_CONTROL_KINEMATIC_OBJECT_HACK: These date members allow an Action
+    // ACTION_CAN_CONTROL_KINEMATIC_OBJECT_HACK: These data members allow an Action
     // to operate on a kinematic object without screwing up our default kinematic integration
     // which is done in the MotionState::getWorldTransform().
     mutable uint32_t _lastKinematicStep;
diff --git a/libraries/physics/src/PhysicalEntitySimulation.cpp b/libraries/physics/src/PhysicalEntitySimulation.cpp
index 8e5248f6a9..daa2b5d954 100644
--- a/libraries/physics/src/PhysicalEntitySimulation.cpp
+++ b/libraries/physics/src/PhysicalEntitySimulation.cpp
@@ -131,10 +131,10 @@ void PhysicalEntitySimulation::takeDeadAvatarEntities(SetOfEntities& deadEntitie
     _deadAvatarEntities.clear();
 }
 
-void PhysicalEntitySimulation::changeEntityInternal(EntityItemPointer entity) {
+void PhysicalEntitySimulation::processChangedEntity(const EntityItemPointer& entity) {
+    EntitySimulation::processChangedEntity(entity);
+
     // queue incoming changes: from external sources (script, EntityServer, etc) to physics engine
-    QMutexLocker lock(&_mutex);
-    assert(entity);
     EntityMotionState* motionState = static_cast<EntityMotionState*>(entity->getPhysicsInfo());
     uint8_t region = _space->getRegion(entity->getSpaceIndex());
     bool shouldBePhysical = region < workload::Region::R3 && entity->shouldBePhysical();
@@ -156,7 +156,6 @@ void PhysicalEntitySimulation::changeEntityInternal(EntityItemPointer entity) {
 
             // remove from the physical simulation
             _incomingChanges.remove(motionState);
-            _physicalObjects.remove(motionState);
             removeOwnershipData(motionState);
             _entitiesToRemoveFromPhysics.insert(entity);
             if (canBeKinematic && entity->isMovingRelativeToParent()) {
@@ -227,44 +226,68 @@ void PhysicalEntitySimulation::prepareEntityForDelete(EntityItemPointer entity)
 }
 // end EntitySimulation overrides
 
-const VectorOfMotionStates& PhysicalEntitySimulation::getObjectsToRemoveFromPhysics() {
-    QMutexLocker lock(&_mutex);
-    for (auto entity: _entitiesToRemoveFromPhysics) {
-        EntityMotionState* motionState = static_cast<EntityMotionState*>(entity->getPhysicsInfo());
-        assert(motionState);
-      // TODO CLEan this, just a n extra check to avoid the crash that shouldn;t happen
-      if (motionState) {
-            _entitiesToAddToPhysics.remove(entity);
-            if (entity->isDead() && entity->getElement()) {
-                _deadEntities.insert(entity);
+void PhysicalEntitySimulation::buildMotionStatesForEntitiesThatNeedThem() {
+    // this lambda for when we decide to actually build the motionState
+    auto buildMotionState = [&](btCollisionShape* shape, EntityItemPointer entity) {
+        EntityMotionState* motionState = new EntityMotionState(shape, entity);
+        entity->setPhysicsInfo(static_cast<void*>(motionState));
+        motionState->setRegion(_space->getRegion(entity->getSpaceIndex()));
+        _physicalObjects.insert(motionState);
+        _incomingChanges.insert(motionState);
+    };
+
+    uint32_t deliveryCount = ObjectMotionState::getShapeManager()->getWorkDeliveryCount();
+    if (deliveryCount != _lastWorkDeliveryCount) {
+        // new off-thread shapes have arrived --> find adds whose shapes have arrived
+        _lastWorkDeliveryCount = deliveryCount;
+        ShapeRequests::iterator requestItr = _shapeRequests.begin();
+        while (requestItr != _shapeRequests.end()) {
+            EntityItemPointer entity = requestItr->entity;
+            EntityMotionState* motionState = static_cast<EntityMotionState*>(entity->getPhysicsInfo());
+            if (!motionState) {
+                // this is an ADD because motionState doesn't exist yet
+                btCollisionShape* shape = const_cast<btCollisionShape*>(ObjectMotionState::getShapeManager()->getShapeByKey(requestItr->shapeHash));
+                if (shape) {
+                    // shape is ready at last!
+                    // But the entity's desired shape might have changed since last requested
+                    // --> rebuild the ShapeInfo to verify hash
+                    // TODO? is there a better way to do this?
+                    ShapeInfo shapeInfo;
+                    entity->computeShapeInfo(shapeInfo);
+                    if (shapeInfo.getHash() != requestItr->shapeHash) {
+                        // bummer, the hashes are different and we no longer want the shape we've received
+                        ObjectMotionState::getShapeManager()->releaseShape(shape);
+                        // try again
+                        shape = const_cast<btCollisionShape*>(ObjectMotionState::getShapeManager()->getShape(shapeInfo));
+                        if (shape) {
+                            buildMotionState(shape, entity);
+                            requestItr = _shapeRequests.erase(requestItr);
+                        } else {
+                            requestItr->shapeHash = shapeInfo.getHash();
+                            ++requestItr;
+                        }
+                    } else {
+                        buildMotionState(shape, entity);
+                        requestItr = _shapeRequests.erase(requestItr);
+                    }
+                } else {
+                    // shape not ready
+                    ++requestItr;
+                }
+            } else {
+                // this is a CHANGE because motionState already exists
+                if (ObjectMotionState::getShapeManager()->hasShapeWithKey(requestItr->shapeHash)) {
+                    entity->markDirtyFlags(Simulation::DIRTY_SHAPE);
+                    _incomingChanges.insert(motionState);
+                    requestItr = _shapeRequests.erase(requestItr);
+                } else {
+                    // shape not ready
+                    ++requestItr;
+                }
             }
-
-            _incomingChanges.remove(motionState);
-            removeOwnershipData(motionState);
-            _physicalObjects.remove(motionState);
-
-            // remember this motionState and delete it later (after removing its RigidBody from the PhysicsEngine)
-            _objectsToDelete.push_back(motionState);
         }
     }
-    _entitiesToRemoveFromPhysics.clear();
-    return _objectsToDelete;
-}
 
-void PhysicalEntitySimulation::deleteObjectsRemovedFromPhysics() {
-    QMutexLocker lock(&_mutex);
-    for (auto motionState : _objectsToDelete) {
-        // someday when we invert the entities/physics lib dependencies we can let EntityItem delete its own PhysicsInfo
-        // until then we must do it here
-        // NOTE: a reference to the EntityItemPointer is released in the EntityMotionState::dtor
-        delete motionState;
-    }
-    _objectsToDelete.clear();
-}
-
-void PhysicalEntitySimulation::getObjectsToAddToPhysics(VectorOfMotionStates& result) {
-    result.clear();
-    QMutexLocker lock(&_mutex);
     SetOfEntities::iterator entityItr = _entitiesToAddToPhysics.begin();
     while (entityItr != _entitiesToAddToPhysics.end()) {
         EntityItemPointer entity = (*entityItr);
@@ -273,7 +296,7 @@ void PhysicalEntitySimulation::getObjectsToAddToPhysics(VectorOfMotionStates& re
             prepareEntityForDelete(entity);
             entityItr = _entitiesToAddToPhysics.erase(entityItr);
         } else if (!entity->shouldBePhysical()) {
-            // this entity should no longer be on the internal _entitiesToAddToPhysics
+            // this entity should no longer be on _entitiesToAddToPhysics
             entityItr = _entitiesToAddToPhysics.erase(entityItr);
             if (entity->isMovingRelativeToParent()) {
                 SetOfEntities::iterator itr = _simpleKinematicEntities.find(entity);
@@ -282,53 +305,149 @@ void PhysicalEntitySimulation::getObjectsToAddToPhysics(VectorOfMotionStates& re
                 }
             }
         } else if (entity->isReadyToComputeShape()) {
-            ShapeInfo shapeInfo;
-            entity->computeShapeInfo(shapeInfo);
-            int numPoints = shapeInfo.getLargestSubshapePointCount();
-            if (shapeInfo.getType() == SHAPE_TYPE_COMPOUND) {
-                if (numPoints > MAX_HULL_POINTS) {
-                    qWarning() << "convex hull with" << numPoints
-                        << "points for entity" << entity->getName()
-                        << "at" << entity->getWorldPosition() << " will be reduced";
+            ShapeRequest shapeRequest(entity);
+            ShapeRequests::iterator  requestItr = _shapeRequests.find(shapeRequest);
+            if (requestItr == _shapeRequests.end()) {
+                // not waiting for a shape (yet)
+                ShapeInfo shapeInfo;
+                entity->computeShapeInfo(shapeInfo);
+                uint32_t requestCount = ObjectMotionState::getShapeManager()->getWorkRequestCount();
+                btCollisionShape* shape = const_cast<btCollisionShape*>(ObjectMotionState::getShapeManager()->getShape(shapeInfo));
+                if (shape) {
+                    EntityMotionState* motionState = static_cast<EntityMotionState*>(entity->getPhysicsInfo());
+                    if (!motionState) {
+                        buildMotionState(shape, entity);
+                    } else {
+                        // Is it possible to fall in here?
+                        // entity shouldn't be on _entitiesToAddToPhysics list if it already has a motionState.
+                        // but just in case...
+                        motionState->setShape(shape);
+                        motionState->setRegion(_space->getRegion(entity->getSpaceIndex()));
+                        _physicalObjects.insert(motionState);
+                        _incomingChanges.insert(motionState);
+                    }
+                } else if (requestCount != ObjectMotionState::getShapeManager()->getWorkRequestCount()) {
+                    // shape doesn't exist but a new worker has been spawned to build it --> add to shapeRequests and wait
+                    shapeRequest.shapeHash = shapeInfo.getHash();
+                    _shapeRequests.insert(shapeRequest);
+                } else {
+                    // failed to build shape --> will not be added
                 }
             }
-            btCollisionShape* shape = const_cast<btCollisionShape*>(ObjectMotionState::getShapeManager()->getShape(shapeInfo));
-            if (shape) {
-                EntityMotionState* motionState = new EntityMotionState(shape, entity);
-                entity->setPhysicsInfo(static_cast<void*>(motionState));
-                _physicalObjects.insert(motionState);
-                result.push_back(motionState);
-                entityItr = _entitiesToAddToPhysics.erase(entityItr);
-
-                // make sure the motionState's region is up-to-date before it is actually added to physics
-                motionState->setRegion(_space->getRegion(entity->getSpaceIndex()));
-            } else {
-                //qWarning() << "Failed to generate new shape for entity." << entity->getName();
-                ++entityItr;
-            }
+            entityItr = _entitiesToAddToPhysics.erase(entityItr);
         } else {
             ++entityItr;
         }
     }
 }
 
-void PhysicalEntitySimulation::setObjectsToChange(const VectorOfMotionStates& objectsToChange) {
+void PhysicalEntitySimulation::buildPhysicsTransaction(PhysicsEngine::Transaction& transaction) {
     QMutexLocker lock(&_mutex);
-    for (auto object : objectsToChange) {
-        _incomingChanges.insert(static_cast<EntityMotionState*>(object));
+    // entities being removed
+    for (auto entity : _entitiesToRemoveFromPhysics) {
+        EntityMotionState* motionState = static_cast<EntityMotionState*>(entity->getPhysicsInfo());
+        if (motionState) {
+            transaction.objectsToRemove.push_back(motionState);
+            _incomingChanges.remove(motionState);
+        }
+        if (_shapeRequests.size() > 0) {
+            ShapeRequest shapeRequest(entity);
+            ShapeRequests::iterator  requestItr = _shapeRequests.find(shapeRequest);
+            if (requestItr != _shapeRequests.end()) {
+                _shapeRequests.erase(requestItr);
+            }
+        }
     }
-}
+    _entitiesToRemoveFromPhysics.clear();
 
-void PhysicalEntitySimulation::getObjectsToChange(VectorOfMotionStates& result) {
-    result.clear();
-    QMutexLocker lock(&_mutex);
-    for (auto stateItr : _incomingChanges) {
-        EntityMotionState* motionState = &(*stateItr);
-        result.push_back(motionState);
+    // entities to add
+    buildMotionStatesForEntitiesThatNeedThem();
+
+    // motionStates with changed entities: delete, add, or change
+    for (auto& object : _incomingChanges) {
+        uint32_t unhandledFlags = object->getIncomingDirtyFlags();
+
+        uint32_t handledFlags = EASY_DIRTY_PHYSICS_FLAGS;
+        bool isInPhysicsSimulation = object->isInPhysicsSimulation();
+        bool shouldBeInPhysicsSimulation = object->shouldBeInPhysicsSimulation();
+        if (!shouldBeInPhysicsSimulation && isInPhysicsSimulation) {
+            transaction.objectsToRemove.push_back(object);
+            continue;
+        }
+
+        bool needsNewShape = object->needsNewShape();
+        if (needsNewShape) {
+            ShapeType shapeType = object->getShapeType();
+            if (shapeType == SHAPE_TYPE_STATIC_MESH) {
+                ShapeRequest shapeRequest(object->_entity);
+                ShapeRequests::iterator  requestItr = _shapeRequests.find(shapeRequest);
+                if (requestItr == _shapeRequests.end()) {
+                    ShapeInfo shapeInfo;
+                    object->_entity->computeShapeInfo(shapeInfo);
+                    uint32_t requestCount = ObjectMotionState::getShapeManager()->getWorkRequestCount();
+                    btCollisionShape* shape = const_cast<btCollisionShape*>(ObjectMotionState::getShapeManager()->getShape(shapeInfo));
+                    if (shape) {
+                        object->setShape(shape);
+                        handledFlags |= Simulation::DIRTY_SHAPE;
+                        needsNewShape = false;
+                    } else if (requestCount != ObjectMotionState::getShapeManager()->getWorkRequestCount()) {
+                        // shape doesn't exist but a new worker has been spawned to build it --> add to shapeRequests and wait
+                        shapeRequest.shapeHash = shapeInfo.getHash();
+                        _shapeRequests.insert(shapeRequest);
+                    } else {
+                        // failed to build shape --> will not be added/updated
+                        handledFlags |= Simulation::DIRTY_SHAPE;
+                    }
+                } else {
+                    // continue waiting for shape request
+                }
+            } else {
+                ShapeInfo shapeInfo;
+                object->_entity->computeShapeInfo(shapeInfo);
+                btCollisionShape* shape = const_cast<btCollisionShape*>(ObjectMotionState::getShapeManager()->getShape(shapeInfo));
+                if (shape) {
+                    object->setShape(shape);
+                    handledFlags |= Simulation::DIRTY_SHAPE;
+                    needsNewShape = false;
+                } else {
+                    // failed to build shape --> will not be added
+                }
+            }
+        }
+        if (!isInPhysicsSimulation) {
+            if (needsNewShape) {
+                // skip it
+                continue;
+            } else {
+                transaction.objectsToAdd.push_back(object);
+                handledFlags = DIRTY_PHYSICS_FLAGS;
+                unhandledFlags = 0;
+            }
+        }
+
+        if (unhandledFlags & EASY_DIRTY_PHYSICS_FLAGS) {
+            object->handleEasyChanges(unhandledFlags);
+        }
+        if (unhandledFlags & (Simulation::DIRTY_MOTION_TYPE | Simulation::DIRTY_COLLISION_GROUP | (handledFlags & Simulation::DIRTY_SHAPE))) {
+            transaction.objectsToReinsert.push_back(object);
+            handledFlags |= HARD_DIRTY_PHYSICS_FLAGS;
+        } else if (unhandledFlags & Simulation::DIRTY_PHYSICS_ACTIVATION && object->getRigidBody()->isStaticObject()) {
+            transaction.activeStaticObjects.push_back(object);
+        }
+        object->clearIncomingDirtyFlags(handledFlags);
     }
     _incomingChanges.clear();
 }
 
+void PhysicalEntitySimulation::handleProcessedPhysicsTransaction(PhysicsEngine::Transaction& transaction) {
+    // things on objectsToRemove are ready for delete
+    for (auto object : transaction.objectsToRemove) {
+        _physicalObjects.remove(object);
+        delete object;
+    }
+    transaction.clear();
+}
+
 void PhysicalEntitySimulation::handleDeactivatedMotionStates(const VectorOfMotionStates& motionStates) {
     bool serverlessMode = getEntityTree()->isServerlessMode();
     for (auto stateItr : motionStates) {
diff --git a/libraries/physics/src/PhysicalEntitySimulation.h b/libraries/physics/src/PhysicalEntitySimulation.h
index 843069e247..817f92cb3c 100644
--- a/libraries/physics/src/PhysicalEntitySimulation.h
+++ b/libraries/physics/src/PhysicalEntitySimulation.h
@@ -13,6 +13,8 @@
 #define hifi_PhysicalEntitySimulation_h
 
 #include <stdint.h>
+#include <map>
+#include <set>
 
 #include <btBulletDynamicsCommon.h>
 #include <BulletCollision/CollisionDispatch/btGhostObject.h>
@@ -70,7 +72,7 @@ protected: // only called by EntitySimulation
     virtual void updateEntitiesInternal(uint64_t now) override;
     virtual void addEntityInternal(EntityItemPointer entity) override;
     virtual void removeEntityInternal(EntityItemPointer entity) override;
-    virtual void changeEntityInternal(EntityItemPointer entity) override;
+    void processChangedEntity(const EntityItemPointer& entity) override;
     virtual void clearEntitiesInternal() override;
 
     void removeOwnershipData(EntityMotionState* motionState);
@@ -79,12 +81,8 @@ protected: // only called by EntitySimulation
 public:
     virtual void prepareEntityForDelete(EntityItemPointer entity) override;
 
-    const VectorOfMotionStates& getObjectsToRemoveFromPhysics();
-    void deleteObjectsRemovedFromPhysics();
-
-    void getObjectsToAddToPhysics(VectorOfMotionStates& result);
-    void setObjectsToChange(const VectorOfMotionStates& objectsToChange);
-    void getObjectsToChange(VectorOfMotionStates& result);
+    void buildPhysicsTransaction(PhysicsEngine::Transaction& transaction);
+    void handleProcessedPhysicsTransaction(PhysicsEngine::Transaction& transaction);
 
     void handleDeactivatedMotionStates(const VectorOfMotionStates& motionStates);
     void handleChangedMotionStates(const VectorOfMotionStates& motionStates);
@@ -98,16 +96,25 @@ public:
     void sendOwnedUpdates(uint32_t numSubsteps);
 
 private:
-    SetOfEntities _entitiesToAddToPhysics;
+    void buildMotionStatesForEntitiesThatNeedThem();
+
+    class ShapeRequest {
+    public:
+        ShapeRequest() { }
+        ShapeRequest(const EntityItemPointer& e) : entity(e) { }
+        bool operator<(const ShapeRequest& other) const { return entity.get() < other.entity.get(); }
+        bool operator==(const ShapeRequest& other) const { return entity.get() == other.entity.get(); }
+        EntityItemPointer entity { nullptr };
+        mutable uint64_t shapeHash { 0 };
+    };
+    SetOfEntities _entitiesToAddToPhysics; // we could also call this: _entitiesThatNeedMotionStates
     SetOfEntities _entitiesToRemoveFromPhysics;
-
-    VectorOfMotionStates _objectsToDelete;
-
-    SetOfEntityMotionStates _incomingChanges; // EntityMotionStates that have changed from external sources
-                                              // and need their RigidBodies updated
-
+    SetOfEntityMotionStates _incomingChanges; // EntityMotionStates changed by external events
     SetOfMotionStates _physicalObjects; // MotionStates of entities in PhysicsEngine
 
+    using ShapeRequests = std::set<ShapeRequest>;
+    ShapeRequests _shapeRequests;
+
     PhysicsEnginePointer _physicsEngine = nullptr;
     EntityEditPacketSender* _entityPacketSender = nullptr;
 
@@ -117,6 +124,7 @@ private:
     workload::SpacePointer _space;
     uint64_t _nextBidExpiry;
     uint32_t _lastStepSendPackets { 0 };
+    uint32_t _lastWorkDeliveryCount { 0 };
 };
 
 
diff --git a/libraries/physics/src/PhysicsEngine.cpp b/libraries/physics/src/PhysicsEngine.cpp
index 4453a7d9f0..976c547c5e 100644
--- a/libraries/physics/src/PhysicsEngine.cpp
+++ b/libraries/physics/src/PhysicsEngine.cpp
@@ -178,8 +178,6 @@ void PhysicsEngine::addObjectToDynamicsWorld(ObjectMotionState* motionState) {
     int32_t group, mask;
     motionState->computeCollisionGroupAndMask(group, mask);
     _dynamicsWorld->addRigidBody(body, group, mask);
-
-    motionState->clearIncomingDirtyFlags();
 }
 
 QList<EntityDynamicPointer> PhysicsEngine::removeDynamicsForBody(btRigidBody* body) {
@@ -252,6 +250,7 @@ void PhysicsEngine::removeSetOfObjects(const SetOfMotionStates& objects) {
         }
         object->clearIncomingDirtyFlags();
     }
+    _activeStaticBodies.clear();
 }
 
 void PhysicsEngine::addObjects(const VectorOfMotionStates& objects) {
@@ -260,35 +259,6 @@ void PhysicsEngine::addObjects(const VectorOfMotionStates& objects) {
     }
 }
 
-VectorOfMotionStates PhysicsEngine::changeObjects(const VectorOfMotionStates& objects) {
-    VectorOfMotionStates stillNeedChange;
-    for (auto object : objects) {
-        uint32_t flags = object->getIncomingDirtyFlags() & DIRTY_PHYSICS_FLAGS;
-        if (flags & HARD_DIRTY_PHYSICS_FLAGS) {
-            if (object->handleHardAndEasyChanges(flags, this)) {
-                object->clearIncomingDirtyFlags();
-            } else {
-                stillNeedChange.push_back(object);
-            }
-        } else if (flags & EASY_DIRTY_PHYSICS_FLAGS) {
-            object->handleEasyChanges(flags);
-            object->clearIncomingDirtyFlags();
-        }
-        if (object->getMotionType() == MOTION_TYPE_STATIC && object->isActive()) {
-            _activeStaticBodies.insert(object->getRigidBody());
-        }
-    }
-    // active static bodies have changed (in an Easy way) and need their Aabbs updated
-    // but we've configured Bullet to NOT update them automatically (for improved performance)
-    // so we must do it ourselves
-    std::set<btRigidBody*>::const_iterator itr = _activeStaticBodies.begin();
-    while (itr != _activeStaticBodies.end()) {
-        _dynamicsWorld->updateSingleAabb(*itr);
-        ++itr;
-    }
-    return stillNeedChange;
-}
-
 void PhysicsEngine::reinsertObject(ObjectMotionState* object) {
     // remove object from DynamicsWorld
     bumpAndPruneContacts(object);
@@ -320,7 +290,6 @@ void PhysicsEngine::processTransaction(PhysicsEngine::Transaction& transaction)
             body->setMotionState(nullptr);
             delete body;
         }
-        object->clearIncomingDirtyFlags();
     }
 
     // adds
@@ -328,34 +297,16 @@ void PhysicsEngine::processTransaction(PhysicsEngine::Transaction& transaction)
         addObjectToDynamicsWorld(object);
     }
 
-    // changes
-    std::vector<ObjectMotionState*> failedChanges;
-    for (auto object : transaction.objectsToChange) {
-        uint32_t flags = object->getIncomingDirtyFlags() & DIRTY_PHYSICS_FLAGS;
-        if (flags & HARD_DIRTY_PHYSICS_FLAGS) {
-            if (object->handleHardAndEasyChanges(flags, this)) {
-                object->clearIncomingDirtyFlags();
-            } else {
-                failedChanges.push_back(object);
-            }
-        } else if (flags & EASY_DIRTY_PHYSICS_FLAGS) {
-            object->handleEasyChanges(flags);
-            object->clearIncomingDirtyFlags();
-        }
-        if (object->getMotionType() == MOTION_TYPE_STATIC && object->isActive()) {
-            _activeStaticBodies.insert(object->getRigidBody());
-        }       
+    // reinserts
+    for (auto object : transaction.objectsToReinsert) {
+        reinsertObject(object);
     }
-    // activeStaticBodies have changed (in an Easy way) and need their Aabbs updated
-    // but we've configured Bullet to NOT update them automatically (for improved performance)
-    // so we must do it ourselves
-    std::set<btRigidBody*>::const_iterator itr = _activeStaticBodies.begin();
-    while (itr != _activeStaticBodies.end()) {
-        _dynamicsWorld->updateSingleAabb(*itr);
-        ++itr;
+
+    for (auto object : transaction.activeStaticObjects) {
+        btRigidBody* body = object->getRigidBody();
+        _dynamicsWorld->updateSingleAabb(body);
+        _activeStaticBodies.insert(body);
     }
-    // we replace objectsToChange with any that failed
-    transaction.objectsToChange.swap(failedChanges);
 }
 
 void PhysicsEngine::removeContacts(ObjectMotionState* motionState) {
diff --git a/libraries/physics/src/PhysicsEngine.h b/libraries/physics/src/PhysicsEngine.h
index 43cc0d2176..d11b52f1af 100644
--- a/libraries/physics/src/PhysicsEngine.h
+++ b/libraries/physics/src/PhysicsEngine.h
@@ -79,11 +79,13 @@ public:
         void clear() {
             objectsToRemove.clear();
             objectsToAdd.clear();
-            objectsToChange.clear();
+            objectsToReinsert.clear();
+            activeStaticObjects.clear();
         }
         std::vector<ObjectMotionState*> objectsToRemove;
         std::vector<ObjectMotionState*> objectsToAdd;
-        std::vector<ObjectMotionState*> objectsToChange;
+        std::vector<ObjectMotionState*> objectsToReinsert;
+        std::vector<ObjectMotionState*> activeStaticObjects;
     };
 
     PhysicsEngine(const glm::vec3& offset);
@@ -97,7 +99,7 @@ public:
     void removeSetOfObjects(const SetOfMotionStates& objects); // only called during teardown
 
     void addObjects(const VectorOfMotionStates& objects);
-    VectorOfMotionStates changeObjects(const VectorOfMotionStates& objects);
+    void changeObjects(const VectorOfMotionStates& objects);
     void reinsertObject(ObjectMotionState* object);
 
     void processTransaction(Transaction& transaction);
diff --git a/libraries/physics/src/ShapeFactory.cpp b/libraries/physics/src/ShapeFactory.cpp
index 5808a539d6..ef5213df8f 100644
--- a/libraries/physics/src/ShapeFactory.cpp
+++ b/libraries/physics/src/ShapeFactory.cpp
@@ -293,6 +293,8 @@ const btCollisionShape* ShapeFactory::createShapeFromInfo(const ShapeInfo& info)
                 radiuses.push_back(sphereData.w);
             }
             shape = new btMultiSphereShape(positions.data(), radiuses.data(), (int)positions.size());
+            const float MULTI_SPHERE_MARGIN = 0.001f;
+            shape->setMargin(MULTI_SPHERE_MARGIN);
         }
         break;
         case SHAPE_TYPE_ELLIPSOID: {
@@ -433,6 +435,8 @@ const btCollisionShape* ShapeFactory::createShapeFromInfo(const ShapeInfo& info)
             }
         }
         break;
+        default:
+        break;
     }
     if (shape) {
         if (glm::length2(info.getOffset()) > MIN_SHAPE_OFFSET * MIN_SHAPE_OFFSET) {
@@ -457,6 +461,8 @@ const btCollisionShape* ShapeFactory::createShapeFromInfo(const ShapeInfo& info)
                 shape = compound;
             }
         }
+    } else {
+        // TODO: warn about this case
     }
     return shape;
 }
@@ -481,3 +487,8 @@ void ShapeFactory::deleteShape(const btCollisionShape* shape) {
     }
     delete nonConstShape;
 }
+
+void ShapeFactory::Worker::run() {
+    shape = ShapeFactory::createShapeFromInfo(shapeInfo);
+    emit submitWork(this);
+}
diff --git a/libraries/physics/src/ShapeFactory.h b/libraries/physics/src/ShapeFactory.h
index 704a7804b3..d23785d513 100644
--- a/libraries/physics/src/ShapeFactory.h
+++ b/libraries/physics/src/ShapeFactory.h
@@ -14,6 +14,8 @@
 
 #include <btBulletDynamicsCommon.h>
 #include <glm/glm.hpp>
+#include <QObject>
+#include <QtCore/QRunnable>
 
 #include <ShapeInfo.h>
 
@@ -22,6 +24,17 @@
 namespace ShapeFactory {
     const btCollisionShape* createShapeFromInfo(const ShapeInfo& info);
     void deleteShape(const btCollisionShape* shape);
+
+    class Worker : public QObject, public QRunnable {
+        Q_OBJECT
+    public:
+        Worker(const ShapeInfo& info) : shapeInfo(info), shape(nullptr) {}
+        void run() override;
+        ShapeInfo shapeInfo;
+        const btCollisionShape* shape;
+    signals:
+        void submitWork(Worker*);
+    };
 };
 
 #endif // hifi_ShapeFactory_h
diff --git a/libraries/physics/src/ShapeManager.cpp b/libraries/physics/src/ShapeManager.cpp
index 8acbe51540..c37f95b5f1 100644
--- a/libraries/physics/src/ShapeManager.cpp
+++ b/libraries/physics/src/ShapeManager.cpp
@@ -12,15 +12,15 @@
 #include "ShapeManager.h"
 
 #include <glm/gtx/norm.hpp>
+#include <QThreadPool>
 
-#include <QDebug>
-
-#include "ShapeFactory.h"
+#include <NumericalConstants.h>
 
 const int MAX_RING_SIZE = 256;
 
 ShapeManager::ShapeManager() {
     _garbageRing.reserve(MAX_RING_SIZE);
+    _nextOrphanExpiry = std::chrono::steady_clock::now();
 }
 
 ShapeManager::~ShapeManager() {
@@ -30,6 +30,10 @@ ShapeManager::~ShapeManager() {
         ShapeFactory::deleteShape(shapeRef->shape);
     }
     _shapeMap.clear();
+    if (_deadWorker) {
+        delete _deadWorker;
+        _deadWorker = nullptr;
+    }
 }
 
 const btCollisionShape* ShapeManager::getShape(const ShapeInfo& info) {
@@ -42,17 +46,84 @@ const btCollisionShape* ShapeManager::getShape(const ShapeInfo& info) {
         shapeRef->refCount++;
         return shapeRef->shape;
     }
-    const btCollisionShape* shape = ShapeFactory::createShapeFromInfo(info);
-    if (shape) {
-        ShapeReference newRef;
-        newRef.refCount = 1;
-        newRef.shape = shape;
-        newRef.key = info.getHash();
-        _shapeMap.insert(hashKey, newRef);
+    const btCollisionShape* shape = nullptr;
+    if (info.getType() == SHAPE_TYPE_STATIC_MESH) {
+        uint64_t hash = info.getHash();
+        const auto itr = std::find(_pendingMeshShapes.begin(), _pendingMeshShapes.end(), hash);
+        if (itr == _pendingMeshShapes.end()) {
+            // start a worker
+            _pendingMeshShapes.push_back(hash);
+            ++_workRequestCount;
+            // try to recycle old deadWorker
+            ShapeFactory::Worker* worker = _deadWorker;
+            if (!worker) {
+                worker = new ShapeFactory::Worker(info);
+            } else {
+                worker->shapeInfo = info;
+                _deadWorker = nullptr;
+            }
+            // we will delete worker manually later
+            worker->setAutoDelete(false);
+            QObject::connect(worker, &ShapeFactory::Worker::submitWork, this, &ShapeManager::acceptWork);
+            QThreadPool::globalInstance()->start(worker);
+        }
+        // else we're still waiting for the shape to be created on another thread
+    } else {
+        shape = ShapeFactory::createShapeFromInfo(info);
+        if (shape) {
+            ShapeReference newRef;
+            newRef.refCount = 1;
+            newRef.shape = shape;
+            newRef.key = info.getHash();
+            _shapeMap.insert(hashKey, newRef);
+        }
     }
     return shape;
 }
 
+const btCollisionShape* ShapeManager::getShapeByKey(uint64_t key) {
+    HashKey hashKey(key);
+    ShapeReference* shapeRef = _shapeMap.find(hashKey);
+    if (shapeRef) {
+        shapeRef->refCount++;
+        return shapeRef->shape;
+    }
+    return nullptr;
+}
+
+bool ShapeManager::hasShapeWithKey(uint64_t key) const {
+    HashKey hashKey(key);
+    const ShapeReference* shapeRef = _shapeMap.find(hashKey);
+    return (bool)shapeRef;
+}
+
+void ShapeManager::addToGarbage(uint64_t key) {
+    // look for existing entry in _garbageRing
+    int32_t ringSize = (int32_t)(_garbageRing.size());
+    for (int32_t i = 0; i < ringSize; ++i) {
+        int32_t j = (_ringIndex + ringSize) % ringSize;
+        if (_garbageRing[j] == key) {
+            // already on the list, don't add it again
+            return;
+        }
+    }
+    if (ringSize == MAX_RING_SIZE) {
+        // remove one
+        HashKey hashKeyToRemove(_garbageRing[_ringIndex]);
+        ShapeReference* shapeRef = _shapeMap.find(hashKeyToRemove);
+        if (shapeRef && shapeRef->refCount == 0) {
+            ShapeFactory::deleteShape(shapeRef->shape);
+            _shapeMap.remove(hashKeyToRemove);
+        }
+        // replace at _ringIndex and advance
+        _garbageRing[_ringIndex] = key;
+        _ringIndex = (_ringIndex + 1) % ringSize;
+    } else {
+        // add one
+        _garbageRing.push_back(key);
+    }
+}
+
 // private helper method
 bool ShapeManager::releaseShapeByKey(uint64_t key) {
     HashKey hashKey(key);
@@ -61,30 +132,7 @@ bool ShapeManager::releaseShapeByKey(uint64_t key) {
         if (shapeRef->refCount > 0) {
             shapeRef->refCount--;
             if (shapeRef->refCount == 0) {
-                // look for existing entry in _garbageRing
-                int32_t ringSize = (int32_t)(_garbageRing.size());
-                for (int32_t i = 0; i < ringSize; ++i) {
-                    int32_t j = (_ringIndex + ringSize) % ringSize;
-                    if (_garbageRing[j] == key) {
-                        // already on the list, don't add it again
-                        return true;
-                    }
-                }
-                if (ringSize == MAX_RING_SIZE) {
-                    // remove one
-                    HashKey hashKeyToRemove(_garbageRing[_ringIndex]);
-                    ShapeReference* shapeRef = _shapeMap.find(hashKeyToRemove);
-                    if (shapeRef && shapeRef->refCount == 0) {
-                        ShapeFactory::deleteShape(shapeRef->shape);
-                        _shapeMap.remove(hashKeyToRemove);
-                    }
-                    // replace at _ringIndex and advance
-                    _garbageRing[_ringIndex] = key;
-                    _ringIndex = (_ringIndex + 1) % ringSize;
-                } else {
-                    // add one
-                    _garbageRing.push_back(key);
-                }
+                addToGarbage(key);
             }
             return true;
         } else {
@@ -153,3 +201,78 @@ bool ShapeManager::hasShape(const btCollisionShape* shape) const {
     }
     return false;
 }
+
+// slot: called when ShapeFactory::Worker is done building shape
+void ShapeManager::acceptWork(ShapeFactory::Worker* worker) {
+    auto itr = std::find(_pendingMeshShapes.begin(), _pendingMeshShapes.end(), worker->shapeInfo.getHash());
+    if (itr == _pendingMeshShapes.end()) {
+        // we've received a shape but don't remember asking for it
+        // (should not fall in here, but if we do: delete the unwanted shape)
+        if (worker->shape) {
+            ShapeFactory::deleteShape(worker->shape);
+        }
+    } else {
+        // clear pending status
+        *itr = _pendingMeshShapes.back();
+        _pendingMeshShapes.pop_back();
+
+        // cache the new shape
+        if (worker->shape) {
+            ShapeReference newRef;
+            // refCount is zero because nothing is using the shape yet
+            newRef.refCount = 0;
+            newRef.shape = worker->shape;
+            newRef.key = worker->shapeInfo.getHash();
+            HashKey hashKey(newRef.key);
+            _shapeMap.insert(hashKey, newRef);
+
+            // This shape's refCount is zero because an object requested it but is not yet using it.  We expect it to be
+            // used later but there is a possibility it will never be used (e.g. the object that wanted it was removed
+            // before the shape could be added, or has changed its mind and now wants a different shape).
+            // Normally zero refCount shapes belong on _garbageRing for possible cleanup but we don't want to add it there
+            // because it might get reaped too soon.  So we add it to _orphans to check later.  If it still has zero
+            // refCount on expiry we will move it to _garbageRing.
+            const int64_t SHAPE_EXPIRY = USECS_PER_SECOND;
+            auto now = std::chrono::steady_clock::now();
+            auto newExpiry = now + std::chrono::microseconds(SHAPE_EXPIRY);
+            if (_nextOrphanExpiry < now) {
+                _nextOrphanExpiry = newExpiry;
+                // check for expired orphan shapes
+                size_t i = 0;
+                while (i < _orphans.size()) {
+                    auto expiry = _orphans[i].expiry;
+                    if (expiry < now) {
+                        uint64_t key = _orphans[i].key;
+                        HashKey hashKey(key);
+                        ShapeReference* shapeRef = _shapeMap.find(hashKey);
+                        if (shapeRef) {
+                            if (shapeRef->refCount == 0) {
+                                // shape unused after expiry
+                                addToGarbage(key);
+                            }
+                        }
+                        _orphans[i] = _orphans.back();
+                        _orphans.pop_back();
+                    } else {
+                        if (expiry < _nextOrphanExpiry) {
+                            _nextOrphanExpiry = expiry;
+                        }
+                        ++i;
+                    }
+                }
+            }
+            _orphans.push_back(KeyExpiry(newRef.key, newExpiry));
+        }
+    }
+    disconnect(worker, &ShapeFactory::Worker::submitWork, this, &ShapeManager::acceptWork);
+
+    if (_deadWorker) {
+        // delete the previous deadWorker manually
+        delete _deadWorker;
+    }
+    // save this dead worker for later
+    worker->shapeInfo.clear();
+    worker->shape = nullptr;
+    _deadWorker = worker;
+    ++_workDeliveryCount;
+}
diff --git a/libraries/physics/src/ShapeManager.h b/libraries/physics/src/ShapeManager.h
index c1fb57e017..1f39fd56be 100644
--- a/libraries/physics/src/ShapeManager.h
+++ b/libraries/physics/src/ShapeManager.h
@@ -12,13 +12,17 @@
 #ifndef hifi_ShapeManager_h
 #define hifi_ShapeManager_h
 
+#include <atomic>
+#include <chrono>
 #include <vector>
 
+#include <QObject>
 #include <btBulletDynamicsCommon.h>
 #include <LinearMath/btHashMap.h>
 
 #include <ShapeInfo.h>
 
+#include "ShapeFactory.h"
 #include "HashKey.h"
 
 // The ShapeManager handles the ref-counting on shared shapes:
@@ -44,7 +48,8 @@
 // entries that still have zero ref-count.
 
 
-class ShapeManager {
+class ShapeManager : public QObject {
+    Q_OBJECT
 public:
 
     ShapeManager();
@@ -52,6 +57,8 @@ public:
 
     /// \return pointer to shape
     const btCollisionShape* getShape(const ShapeInfo& info);
+    const btCollisionShape* getShapeByKey(uint64_t key);
+    bool hasShapeWithKey(uint64_t key) const;
 
     /// \return true if shape was found and released
     bool releaseShape(const btCollisionShape* shape);
@@ -64,8 +71,14 @@ public:
     int getNumReferences(const ShapeInfo& info) const;
     int getNumReferences(const btCollisionShape* shape) const;
     bool hasShape(const btCollisionShape* shape) const;
+    uint32_t getWorkRequestCount() const { return _workRequestCount; }
+    uint32_t getWorkDeliveryCount() const { return _workDeliveryCount; }
+
+protected slots:
+    void acceptWork(ShapeFactory::Worker* worker);
 
 private:
+    void addToGarbage(uint64_t key);
     bool releaseShapeByKey(uint64_t key);
 
     class ShapeReference {
@@ -76,10 +89,24 @@ private:
         ShapeReference() : refCount(0), shape(nullptr) {}
     };
 
+    using TimePoint = std::chrono::time_point<std::chrono::steady_clock>;
+    class KeyExpiry {
+    public:
+        KeyExpiry(uint64_t k, std::chrono::time_point<std::chrono::steady_clock> e) : expiry(e), key(k) {}
+        TimePoint expiry;
+        uint64_t key;
+    };
+
     // btHashMap is required because it supports memory alignment of the btCollisionShapes
     btHashMap<HashKey, ShapeReference> _shapeMap;
     std::vector<uint64_t> _garbageRing;
+    std::vector<uint64_t> _pendingMeshShapes;
+    std::vector<KeyExpiry> _orphans;
+    ShapeFactory::Worker* _deadWorker { nullptr };
+    TimePoint _nextOrphanExpiry;
     uint32_t _ringIndex { 0 };
+    std::atomic_uint _workRequestCount { 0 };
+    std::atomic_uint _workDeliveryCount { 0 };
 };
 
 #endif // hifi_ShapeManager_h
diff --git a/libraries/shared/src/HashKey.cpp b/libraries/shared/src/HashKey.cpp
index 488eccb1bf..8c5303028b 100644
--- a/libraries/shared/src/HashKey.cpp
+++ b/libraries/shared/src/HashKey.cpp
@@ -51,15 +51,15 @@ float HashKey::getNumQuantizedValuesPerMeter() {
     return QUANTIZED_VALUES_PER_METER;
 }
 
-void HashKey::hashUint64(uint64_t data) {
+void HashKey::Hasher::hashUint64(uint64_t data) {
     _hash += squirrel3_64(data, ++_hashCount);
 }
 
-void HashKey::hashFloat(float data) {
+void HashKey::Hasher::hashFloat(float data) {
     _hash += squirrel3_64((uint64_t)((int64_t)(data * QUANTIZED_VALUES_PER_METER)), ++_hashCount);
 }
 
-void HashKey::hashVec3(const glm::vec3& data) {
+void HashKey::Hasher::hashVec3(const glm::vec3& data) {
     _hash += squirrel3_64((uint64_t)((int64_t)(data[0] * QUANTIZED_VALUES_PER_METER)), ++_hashCount);
     _hash *= squirrel3_64((uint64_t)((int64_t)(data[1] * QUANTIZED_VALUES_PER_METER)), ++_hashCount);
     _hash ^= squirrel3_64((uint64_t)((int64_t)(data[2] * QUANTIZED_VALUES_PER_METER)), ++_hashCount);
diff --git a/libraries/shared/src/HashKey.h b/libraries/shared/src/HashKey.h
index 446eb4c25f..071b162a50 100644
--- a/libraries/shared/src/HashKey.h
+++ b/libraries/shared/src/HashKey.h
@@ -30,6 +30,18 @@
 
 class HashKey {
 public:
+    class Hasher {
+    public:
+        Hasher() {}
+        void hashUint64(uint64_t data);
+        void hashFloat(float data);
+        void hashVec3(const glm::vec3& data);
+        uint64_t getHash64() const { return _hash; }
+    private:
+        uint64_t _hash { 0 };
+        uint8_t _hashCount { 0 };
+    };
+
     static float getNumQuantizedValuesPerMeter();
 
     HashKey() {}
@@ -39,16 +51,9 @@ public:
     bool equals(const HashKey& other) const { return _hash == other._hash; }
     int32_t getHash() const { return (int32_t)((uint32_t)_hash); }
 
-    // These methods for accumulating a hash.
-    void hashUint64(uint64_t data);
-    void hashFloat(float data);
-    void hashVec3(const glm::vec3& data);
-
     uint64_t getHash64() const { return _hash; }
-
 private:
     uint64_t _hash { 0 };
-    uint8_t _hashCount { 0 };
 };
 
 #endif // hifi_HashKey_h
diff --git a/libraries/shared/src/ShapeInfo.cpp b/libraries/shared/src/ShapeInfo.cpp
index bf51e455c5..1b9054c4d6 100644
--- a/libraries/shared/src/ShapeInfo.cpp
+++ b/libraries/shared/src/ShapeInfo.cpp
@@ -273,18 +273,18 @@ float ShapeInfo::computeVolume() const {
 uint64_t ShapeInfo::getHash() const {
     // NOTE: we cache the key so we only ever need to compute it once for any valid ShapeInfo instance.
     if (_hash64 == 0 && _type != SHAPE_TYPE_NONE) {
-        HashKey hashKey;
+        HashKey::Hasher hasher;
         // The key is not yet cached therefore we must compute it.
 
-        hashKey.hashUint64((uint64_t)_type);
+        hasher.hashUint64((uint64_t)_type);
         if (_type == SHAPE_TYPE_MULTISPHERE) {
             for (auto &sphereData : _sphereCollection) {
-                hashKey.hashVec3(glm::vec3(sphereData));
-                hashKey.hashFloat(sphereData.w);
+                hasher.hashVec3(glm::vec3(sphereData));
+                hasher.hashFloat(sphereData.w);
             }
         } else if (_type != SHAPE_TYPE_SIMPLE_HULL) {
-            hashKey.hashVec3(_halfExtents);
-            hashKey.hashVec3(_offset);
+            hasher.hashVec3(_halfExtents);
+            hasher.hashVec3(_offset);
         } else {
             // TODO: we could avoid hashing all of these points if we were to supply the ShapeInfo with a unique
             // descriptive string.  Shapes that are uniquely described by their type and URL could just put their
@@ -294,7 +294,7 @@ uint64_t ShapeInfo::getHash() const {
             const int numPoints = (int)points.size();
 
             for (int i = 0; i < numPoints; ++i) {
-                hashKey.hashVec3(points[i]);
+                hasher.hashVec3(points[i]);
             }
         }
 
@@ -302,19 +302,19 @@ uint64_t ShapeInfo::getHash() const {
         if (!url.isEmpty()) {
             QByteArray baUrl = url.toLocal8Bit();
             uint32_t urlHash = qChecksum(baUrl.data(), baUrl.size());
-            hashKey.hashUint64((uint64_t)urlHash);
+            hasher.hashUint64((uint64_t)urlHash);
         }
 
         if (_type == SHAPE_TYPE_COMPOUND || _type == SHAPE_TYPE_SIMPLE_COMPOUND) {
             uint64_t numHulls = (uint64_t)_pointCollection.size();
-            hashKey.hashUint64(numHulls);
+            hasher.hashUint64(numHulls);
         } else if (_type == SHAPE_TYPE_MULTISPHERE) {
             uint64_t numSpheres = (uint64_t)_sphereCollection.size();
-            hashKey.hashUint64(numSpheres);
+            hasher.hashUint64(numSpheres);
         } else if (_type == SHAPE_TYPE_SIMPLE_HULL) {
-            hashKey.hashUint64(1);
+            hasher.hashUint64(1);
         }
-        _hash64 = hashKey.getHash64();
+        _hash64 = hasher.getHash64();
     }
     return _hash64;
 }
diff --git a/libraries/entities/src/SimulationFlags.h b/libraries/shared/src/SimulationFlags.h
similarity index 68%
rename from libraries/entities/src/SimulationFlags.h
rename to libraries/shared/src/SimulationFlags.h
index c45b333b29..9dbb719af2 100644
--- a/libraries/entities/src/SimulationFlags.h
+++ b/libraries/shared/src/SimulationFlags.h
@@ -12,6 +12,17 @@
 #ifndef hifi_SimulationFlags_h
 #define hifi_SimulationFlags_h
 
+const uint8_t YIELD_SIMULATION_PRIORITY = 1;
+const uint8_t VOLUNTEER_SIMULATION_PRIORITY = YIELD_SIMULATION_PRIORITY + 1;
+const uint8_t RECRUIT_SIMULATION_PRIORITY = VOLUNTEER_SIMULATION_PRIORITY + 1;
+
+const uint8_t SCRIPT_GRAB_SIMULATION_PRIORITY = 128;
+const uint8_t SCRIPT_POKE_SIMULATION_PRIORITY = SCRIPT_GRAB_SIMULATION_PRIORITY - 1;
+
+const uint8_t PERSONAL_SIMULATION_PRIORITY = SCRIPT_GRAB_SIMULATION_PRIORITY;
+const uint8_t AVATAR_ENTITY_SIMULATION_PRIORITY = PERSONAL_SIMULATION_PRIORITY;
+
+
 namespace Simulation {
     const uint32_t DIRTY_POSITION = 0x0001;
     const uint32_t DIRTY_ROTATION = 0x0002;
@@ -29,13 +40,14 @@ namespace Simulation {
     const uint32_t DIRTY_SIMULATION_OWNERSHIP_PRIORITY = 0x2000; // our own bid priority has changed
 
     // bits 17-32 are reservied for special flags
-    const uint32_t SPECIAL_FLAGS_NO_BOOTSTRAPPING = 0x10000;
+    const uint32_t SPECIAL_FLAG_NO_BOOTSTRAPPING = 0x10000;
+    const uint32_t SPECIAL_FLAG_IN_PHYSICS_SIMULATION = 0x20000;
 
     const uint32_t DIRTY_TRANSFORM = DIRTY_POSITION | DIRTY_ROTATION;
     const uint32_t DIRTY_VELOCITIES = DIRTY_LINEAR_VELOCITY | DIRTY_ANGULAR_VELOCITY;
-    const uint32_t SPECIAL_FLAGS = SPECIAL_FLAGS_NO_BOOTSTRAPPING;
+    const uint32_t SPECIAL_FLAGS_MASK = SPECIAL_FLAG_NO_BOOTSTRAPPING | SPECIAL_FLAG_IN_PHYSICS_SIMULATION;
 
-    const uint32_t DIRTY_FLAGS = DIRTY_POSITION |
+    const uint32_t DIRTY_FLAGS_MASK = DIRTY_POSITION |
       DIRTY_ROTATION |
       DIRTY_LINEAR_VELOCITY |
       DIRTY_ANGULAR_VELOCITY |
diff --git a/libraries/workload/src/workload/View.cpp b/libraries/workload/src/workload/View.cpp
index 8cb593d2a7..a11b1890fd 100644
--- a/libraries/workload/src/workload/View.cpp
+++ b/libraries/workload/src/workload/View.cpp
@@ -37,8 +37,8 @@ View View::evalFromFrustum(const ViewFrustum& frustum, const glm::vec3& offset)
 
 Sphere View::evalRegionSphere(const View& view, float originRadius, float maxDistance) {
     float radius = (maxDistance + originRadius) / 2.0f;
-    float center = radius - originRadius;
-    return Sphere(view.origin + view.direction * center, radius);
+    float distanceToCenter = radius - originRadius;
+    return Sphere(view.origin + view.direction * distanceToCenter, radius);
 }
 
 void View::updateRegionsDefault(View& view) {