First of all, I promise that this isn't one of those stupid things where you stare at a picture for several seconds, only to have a scary face pop-up and scare the hell out of you! Just look at the picture below, specifically at the NASA logo on the space shuttle's left wing. Relax when you do so. Don't force it. Look at the black and white image for around 10 seconds, then click on the picture and look at the other version for around 30 seconds, again starting at the NASA logo. Then (without looking away) click the picture again... whoa!

Picture by NASA (public domain); illusion created by Jim Cofer

Wanna know how to make these illusions yourself? Click here!