Also Watch :charlie chaplin mask optical illusion, another rotating head illusion
This is an animation of a rotating (anti-clock wise) hollow mask. At the moment you see the back of this hollow mask (so that the hollow side is pointing to you) something surprising happens. It doesn't look hollow, rather it looks like a normal mask - rotating the other way (clock wise)!
The most probable reason is that our vision doesn't accept hollow faces (?).
BTW, Rotating Mask Illusion is designed by Mask of Love Illusion fame Gianni A. Sarcone.