Give her one clue, which leg she stands on, and she can spin only one way: on her left leg (L) clockwise, on her right (R) the other way. The two take turns every 6 seconds. (Clues added by Matthew Lewis, CC BY-SA 3.0.)
Two pictures in one
Spinning dancer
Which way is she spinning?
Either way. Look at her foot on the floor, or blink, and she may switch direction.
Why? A silhouette has no clues to tell front from back, so both directions fit. Your brain chooses one, and can change its mind.
Picture: Nobuyuki Kayahara, CC BY-SA 3.0 · Wikipedia(opens in a new tab)