This Hollow Mask Illusion shows a mask of a face rotating in circles. Each time the mask turns from the outer face to the inner face, I only get a glimpse of the inside before my eyes trick me and the mask protrudes outwards again. No matter how hard I try, this optical illusion gets the best of me each time. Trippy!
This video demonstrates the hollow mask illusion, in which a rotating hollow mask appears as if the inner surface is protruding out. The explanation is when the mask is facing you, the eyes aren't picking up enough visual information to be able to tell if it's the inside surface or the outside. As your brain expects to see the outside of a face and never the inner surface, it constructs the 3D appearance of it protruding out, resulting in your perception of the face pointing at you. Only when it's rotated does the brain suddenly get enough information to indicate that it's the inner surface, resulting in you having a sharp change in perspective as it corrects itself. It's quite eerie, and no matter how many times you watch you can't stop but perceive the inner surface as the outer one.