Isn't this fascinating?
It's an optical illusion where the lady can appear to be spinning in either direction. One site suggests that people who see her spinning clockwise are governed by their right brain, the artistic half, whilst those seeing her spinning anti-clockwise are governed by the pragmatic left brain.
However, the right-brain left-brain theory has largely been disproved, as the brain uses both sides to undertake most tasks. Here's an explanation of how it works, plus you can move on to the 'next random illusion.'
If you can only see her going in one direction and you're having difficulty getting her to go the other way, try staring at the shadow of her foot for a moment and slowly looking up again. It might take a few attempts, but with practice you can get her to switch directions at will.