Online optical illusions make your brain ache...
Doing the weekly WebTwitcher shop this Saturday I stumbled upon one of those 80s-tastic poster shops (you know the sort...always full of Monet prints and pictures of kittens - usually next to Sainsburys) and my gaze fell on an "if you stare hard enough at it you'll see the picure" image. Which got me looking on the web for sites with optical illusions.
Low and behold I have found Michael Bach's Optical Illusions and Visual Phenomina. After staring at the screen for hours on end, I think I need a lie down. WebTwitcher cannot be held responsible for head/eye ache after visiting the site...but it's definitely worth checking out! The rotating faces are just freaky.