A ring of magenta splodges. The splodges flick off momentarily in sequence. Stare at the screen long enough and you will see a green dot moving around the circle (it's an afterimage of the magenta). So far so interesting. Stare at it even longer, and let your eyes relax and I kid you not, the magenta splodges disappear, and all you can see is the green dot moving on its own! Can you get yourself to that state?
More optical illustions here, many of them equally striking. If you find any that you like, let me know.