Watch a fascinating illusion in motion
(courtesy Richard Gregory)

Mike May cannot readily distinguish between the first (normal) face and the second face, in which the eyes and mouth have been inverted. The reason is one of the great mysteries explained by his story.

Note that when the images are flipped upside down, the second faces become more normal looking to us. That’s also part of the mystery.

Nearly all observers perceive the monster in the rear to be much larger. In fact, they are identical in size. Note, also, that the monster doing the chasing appears aggressive or angry, while the one being chased appears terrified. In fact, their faces are identical. Unlike the normally sighted, Mike May rightly perceives the monsters’ size and faces to be identical.
(courtesy Roger Shepard)

To normally sighted observers, the tabletops appear to have entirely different dimensions. To May, they appear identical.
(courtesy Roger Shepard)

Parallel lines appear to converge in the distance to the normally sighted, but not to Mike May, who sees them correctly as forever parallel. It’s not his eye that’s seeing things properly, it’s his brain.