I just had to try this, so printed out and spent 5 minutes cutting and sticking with the 3yr old.Here's an optical illusion you can print out and put on your desk at work...
http://www.grand-illusions.com/opticalillusions/three_dragons/
There's a video demonstrating it here
It's brilliant fun as your mind interprets the visual input and converts it into 3d. It really does look like the head follows you around

P