ok, I was going to post this immediately after I got the thread up because it requires extra direction, but It went into moderation and I forgot. So here goes, one of my favorite optical illusions:

<div align="center">THE ECLIPSE OF MARS
See a new colour you've never seen before!!
at least never before on your monitor


 Stare at the white dot in the center of the red circle. The longer - the better (two minutes and you'll get a much stronger effect). Always try to keep focused on the white dot. It'll be worth it.
Soon after staring, you'll start to see a thin rim of light around the edge. Don't stop staring though yet! Wait another minute - keeping your head perfectly still.
Once you've done this, very slowly - move your head backwards - making sure to keep your eyes focused on the dot at all times. The circle's rim will glow brilliantly with true Cyan! Keep on moving your head slowly backwards, and witness the Eclipse of Mars!...