It's a fix!
If you focus on the angle of her head, she has it tilted to the left when she appears to be going anti-clockwise, and the right when she appears to be going clockwise.
Her head should always be tilted the same way.
I must admit it had me going.
Edit: also focus on the arm which is highest. You'll spot the change.
(, Wed 25 Feb 2009, 11:15, Reply)
No it ain't.
The differences you described are part of the illusion. Your brain interprets the 3D image and you either perceive her as rotating one way or the other - this affects the perceived positioning of her head and arm.
Tried it ages ago with a few people in the office. Some saw it going clockwise, some anti-clockwise. At the same time.
It's mental. But it's a genuine illusion.
(, Wed 25 Feb 2009, 11:36, Reply)