Found this gif image via tumblr:
|Click on the image|
"If your eyes follow the movement of the rotating pink dot, the dots will remain only one color - pink.
However if you stare at the black “+” in the center, the moving dot turns to green.
Now, concentrate on the black “+” in the center of the picture.
After a short period, all the pink dots will slowly disappear, and you will only see only a single green dot rotating."
Interesting huh? I stared at it for a good whole minute, it's kind of hypnotizing.