Ever had a gorilla follow you around the room? The Following Gorilla from the Natural History Museum is an amazing optical illusion, where the face appears to follow you as you move around the room.
So, how does the Following Gorilla work? Our brain makes assumptions about whatever we see. So when it sees the face, it treats it like a typical face that it has experience of. The nose will be the nearest part to us and the face is convex. However in this case that is not true, as the face is actually concave in shape. Our brain cannot understand this and as a result a rather strange illusion takes place where the face appears to be following us around the room.