illusion

Follow the movement of the pink dot for few complete rotations and then
look steadily at the black cross in the middle. You will notice a green dot that will 
erase all pink dots from the image and when you move your eyes slightly away you will see an after effect, a circle with green dots.


I like this illusion because when you focus on the cross the moving circle changes color and turns into green! It's also interesting that has an after effect. 

Here's the link: http://www.scientificpsychic.com/graphics/