The spinning dancer

The spinning dancer appearsz to move both clockwise and counter clock wise

 If the foot touching the ground is perceived to be the left foot, the dancer appears to be spinning clockwise (if seen from above); if it is taken to be the right foot, then she appears to be spinning counter clockwise.

The Spinning Dancer, also known as the silhouette illusion, is a kinetic, bistableoptical illusion resembling a pirouetting female dancer. The illusion, created by web designer Nobuyuki Kayahara,^[1][2] involves the apparent direction of motion of the figure. Some observers initially see the figure as spinning clockwise and some counterclockwise.

The illusion derives from the lack of visual cues for depth. For instance, her arms could be swinging either closer to the viewer and to the left or farther from the viewer and to the left, and hence with her circling clockwise or counter-clockwise on either her left or right foot. She changes leg because she is facing either towards or away from the observer, there being no surface features on the silhouette to indicate at any point which side of her is presented: the least ambiguous positions are her profiles when she is on either side of her circle, though it's still not known whether the foreground or background leg is on the floor, and from where she moves indeterminately either on the near or far arc across to the other profile.

There are other optical illusions that originate from the same or similar kind of visual ambiguity. One example is the Necker Cube.

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