Your eyes are lying

Cool optical illusion trick.

Stare at the crosshairs in the middle of the picture.

Soon you will see a moving green dot. Except there is no green dot, because its only an after image temporarily burnt into you retina.

Keep staring. Slowing all the purple dots will fade until they disappear completely!

After 20 minutes of this you will never be able to see the color purple again.

After 30 minutes you will lose the ability to pronounce the letter "l" and will have a strange craving for McDonald's.

Or at least thats what happened to me.