1.- Click on the link below 
2.- Then "click me to get trippy", 
3.- Look at the center of the screen for 
30 seconds (no cheating), and then 
4.- Look at your hand holding the mouse, without moving it away from the mouse.

You'll be shocked at what you see.

( it is called "cenesthetic hallucination")

http://www.neave.com/strobe/