I found this on the web , its a interesting optical illusion that
illustrates how the brain can be fooled check it out.

http://www.patmedia.net/marklevinson/cool/cool_illusion.html

Very cool.

COOL........

Very groovy - anyone know why it works? something to do with you interpretting the pink dots as an after image perhaps abd mentally editting them away?

The pink dots create a green afterimage. The rotating effect is caused by a disappearing pink dot; one disappears, then comes back and the next blinks out and comes back. When you stare at the center long enough, you get an afterimage green dot that stays when the pink dot vanishes. The other dots slowly vanish due to eye fatigue from staring at the one spot so long.

The eye fatigue part is a surmise on my part, but I think that's what's going on there. Either that or it's the brain reinterpreting things as a green dot rotating around and thus filtering out the pink dots, viewing them as afterimages. I'm leaning heavily toward eye fatigue, however.

Great stuff! thanks

Worth going to the source for the "how does"

http://www.michaelbach.de/ot/col_lilacChaser/index.html