[Solved] Animation sprite go under the ground

Hi all !

I'm a newbie with Construct2 and here is my first unsolved problem :

The monsters on my game goes from the right to left on a platform, but the animation (who's composed of two frames) looks really strange, a part of the monster is under the ground during the frame 1, and not on the frame 2.

I've checked that the origin points are similar, it's ok.

The width and height of the two frames are similar too.

Anyone got an idea for me ?

Thanks a lot !

Oh and btw here is a copy of my project

wilfryed.free.fr/platform.capx

I dunno why i don't see anymore the reply of one of you, but anyways thankyou !

The collision mask was the solution !