This is truly something you MUST do.

Ok, so this is not one of those "look at this for a long time and something scary jumps out" kind of things, because I HATE those. I pee myself. literally. That being said, this black and white pinwheel animation does something cool. Go to the link and after it's all loaded up and spinning smoothly, make sure you can see the whole pinwheel (F11 for fullscreen if you want), and just stare at the center white dot for a good 30 seconds or so. Then look at an object on your desk, or a picture or something. You'll see. It's awesome.

For real, this isn't a trick, just an experiment on perception. Hey while you're at it, visit the whole site!