# BABYLON.PhysicsImpostor.registerOnPhysicsCollide issue, code not called in all cases

**URL:** <https://forum.babylonjs.com/t/babylon-physicsimpostor-registeronphysicscollide-issue-code-not-called-in-all-cases/19176>\
**Category:** Bugs\
**Created:** [March 15, 2021, 2:13am UTC](https://forum.babylonjs.com/t/babylon-physicsimpostor-registeronphysicscollide-issue-code-not-called-in-all-cases/19176 "2021-03-15T02:13:28Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![bjornbacklund](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/bjornbacklund/32/14097_2.png) [@bjornbacklund](https://forum.babylonjs.com/u/bjornbacklund)\
**Post date:** [March 15, 2021, 2:13am UTC](https://forum.babylonjs.com/t/babylon-physicsimpostor-registeronphysicscollide-issue-code-not-called-in-all-cases/19176/1 "2021-03-15T02:13:28Z")

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I can’t figure out why the “on collision” event handler is never called in some cases in this pretty simple example:  
[https://playground.babylonjs.com/#HA35TT#33](https://playground.babylonjs.com/#HA35TT#33)

The sphere clearly collides with both the bounding box and the small cubes but a collision with a cube is not causing the collision event handler to fire. I have been staring at the code for hours…

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**Author:** ![Cedric](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/cedric/32/2742_2.png) [@Cedric](https://forum.babylonjs.com/u/Cedric)\
**Post date:** [March 15, 2021, 9:30am UTC](https://forum.babylonjs.com/t/babylon-physicsimpostor-registeronphysicscollide-issue-code-not-called-in-all-cases/19176/2 "2021-03-15T09:30:32Z")

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Let me take a look

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**Author:** ![Cedric](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/cedric/32/2742_2.png) [@Cedric](https://forum.babylonjs.com/u/Cedric)\
**Post date:** [March 15, 2021, 10:02am UTC](https://forum.babylonjs.com/t/babylon-physicsimpostor-registeronphysicscollide-issue-code-not-called-in-all-cases/19176/3 "2021-03-15T10:02:21Z")

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@bjornbacklund The list of boxes for collision callback was incorrect. You used the meshes instead of the impostors.

Fixed here:

[bingo | Babylon.js Playground](https://playground.babylonjs.com/#HA35TT#34)

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**Author:** ![bjornbacklund](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/bjornbacklund/32/14097_2.png) [@bjornbacklund](https://forum.babylonjs.com/u/bjornbacklund)\
**Post date:** [March 15, 2021, 12:43pm UTC](https://forum.babylonjs.com/t/babylon-physicsimpostor-registeronphysicscollide-issue-code-not-called-in-all-cases/19176/4 "2021-03-15T12:43:42Z")

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Oh, thank you. Feeling pretty embarrassed…