This is one of the most amazing illusions. Keep staring at the blue dot in the middle of the picture. The blue dot will shrink slowly and then disappear completely ! This is due to the color receptors in your eyes getting tired.
PS, sorry about a few images not working in this thread any moor. I had a lot of crap in my photobucket a while ago and just deleted everything in there and did not think about stuff like what is in this thread here.