Stereograms

Its them pictures where they are like loads of dots and stuff, and you stare at them and then a picture, like, arrives in your head - Stereogram Page.

This one is very cool, almost makes you wonder if there would be a way to invoke mind control by having a certain picture.

For fun why not change your monitor to 60Hz and really screw your eyes up.

(that was a joke, its bad enough staring at the monitor at 85Hz)