Check out this illusion over at Cognitive Daily, along with all the explanation that goes with it.
I think illusions are pretty neat. They are also a reminder to not trust what you think you are seeing, since our vision is relative and we also see patterns because we impress them on data.
Very cool! It reminds me of a classic chessboard illusion, which can be seen at the link here .
I saw this chessboard illusion at a talk by Eric Mazur, in which he displayed the picture on a transparency (i.e. no possibility for computer fakery). He sliced the transparency along the checkerboard, and showed that the ‘a’ and ‘b’ squares appeared different until the very moment they were aligned on the projector!