The Spinning Dancer Illusion

I saw this illusion a few years ago.  At first I suspected the animation caused the girl to alternately spin clockwise then stop and spin counterclockwise.  I tested this suspicion with my wife. We both watched at the same time. 

At first I saw the girl spin the way my wife saw it.  Then the girl changed the direction of her spin for me while not for my wife.  Then she changed again.  Sometimes we saw the same thing other times we saw the opposite. This difference in our view of which direction she was spinning proved it was a real optical illusion and not a trick in the animation.
Here she is:

Image via Wikipedia

 From Wikipedia:

The Spinning Dancer is a kinetic, bistable optical illusion resembling a pirouetting female dancer. Some observers initially see the figure as spinning clockwise and some counterclockwise. Additionally, some may see the figure suddenly spin in the opposite direction. The illusion derives from an inherent ambiguity from the lack of visual cues for depth.

Let me know how this turned out for you. 
Have any optical illusions you'd like to share?