Trying to make a sphere fall trough an animated opening hole in mesh. Help? I'm trying to make a hole open up in a primitive, in this case I hooked the vertices of a hole in a flattened cube. The scale animates so that the inner hole opens after a sphere lands on the cube. 

Why does the sphere not fall through the hole? Is there a different way I should be doing this? 
(The image below should be an animated gif)
After setting Rigid Body Collisions to Mesh you need to check Deforming. See my settings below.