Its Friday and on top Friday the 13th. So here are 2 optical illusions to keep you busy.
1) The Spinning Woman:
http://flavor8.com/index.php/2007/06/26/spinning-woman-optical-illusion/
2) Shake
http://www.jwbjerk.com/wp-content/uploads/2006/10/shake.gif
In second link you can actually sense the motion even though its a static image. By changing colors, the illusion of motion can be removed.
First one is not an illusion at all, it smartly changes the spinning direction randomly.
First one is an illusion. I can make the lady go clockwise for as long as I want it as long as I do not look below at her shadow.
Once I look at her shadow and imagine her going counterclockwise she does go counter clock wise.