There's a new educational toy, called Spin Science.
It features a bizarre optical illusion that we wanted to show to you, but first, you need to get close to your screen... So it fills most of your field of vision.
Just click on the attached video, and stare at the center of the spiral. Concentrate and try to lose yourself in the tunnel effect. It looks like your going down a well. Keep focusing, then, suddenly look at the back of your hand.
Your hand should look like it's boiling, with wavy lines over it.
Here's why: the spiral fatigues your visual system in one direction, when you look at your hand... Then you see the opposite effect.