An illusion of a portrait. It holds your attention and makes you examine it. At first the man's face appears to look like it's only half of his face is showing, but once you look at it, you notice that it's also a profile view of the man's face. I think it's a clever and classic design example.
COOL! The universe has its secrets. Extra dimensions of space might be one of them. If so, the universe has been hiding those dimensions, protecting them, keeping them coyly under wraps. From a casual glance, you would never suspect a thing. It's hubris to think that the way we see things is everything there is. -Lisa Randall, theoretical physicist via She Sings to the Stars