Check out these Cool Optical Illusions I stumbled upon:
source: http://mightyillusions.blogspot.com/2006/03/chalk-drawing-illusions.html
[img]http://img369.imageshack.us/img369/9317/aaportab2228yn.jpg[/img]
[img]http://img66.imageshack.us/img66/8262/3droom018uh.jpg[/img]