Here's a previously unknown illusion discovered recently by David O'Reilly. What you see above is just an animated gif of a white grid on a black background, rotating uniformly about its center. Yet if you look at it, you will see what appear to be a number of localized, roughly circular grids rotating independently. O'Reilly has created various versions of the illusion, by varying grid size and rate of rotation, and some of them produce so many localized rotations that you appear to be looking at a seething fluid surface!

Illusion 1, Illusion 25, Illusion 50, Illusion 75, Illusion 110, Illusion 120, Illusion 130, Illusion 140, Illusion 150, Illusion 160, Illusion 170, Illusion 180