‘The pinwheel-like drawing above is nothing but black and white lines. When you look at it the right way, though, something strange and beautiful happens: it begins to flicker. You may think it’s just a regular old optical illusion at first, but actually, you’re looking at your very own brain waves.

To see the optical illusion takes a little bit of work. Look at the pinwheel shape and then stare at a spot that’s just a few inches away from it. When the pinwheel is in your peripheral vision, you should start to see the center flicker, kind of like a really bright star does. The effect also works as an afterimage. So once you find a spot that gets the flicker going, stare at it for about a minute and then look at a blank white wall. You’ll see the inverse image of the pinwheel, flicker and all.’ (Gizmodo).