This is a very interesting image I’ve received a lot of time ago in an e-mail. I’ve been searching a bit but couldn’t find the original creator.
The special thing about this picture is that, when you look at it for the first time, it will be spinning either clockwise or counter-clockwise, but if you keep focusing, you’ll watch it rotating to the oposite direction or even bouncing between sides (half circles), either looking front or back.
It’s a good excercise to be mastered.
I’ve prepared a slower version, just in case you prefer.
Go back to the original version.