You're definately going to want to do an RC after you try this. Open the page, and when the wheel starts rotating, stare at the center of it for about 30-60 seconds. Then look at your hand, or a book or something like that.
http://www.klabaster.com/pinwheel.htm

Speaking of illusions, does anyone like stereograms such as the ones found on eyetricks.com? I'm yet to find anyone but myself who knows how to "use" them....