If you see the dancer spinning clockwise it means you’re using the right half of your brain. If she spins counter-clockwise it means you’re using the left.
The theory: by watching the direction of her spin, we can determine which half of our brains we’re using.
Or maybe it’s just a random optical illusion? Who knows?
The interesting thing = some of us see her spinning one direction, some the other, while some see her change directions and others, for the life of them, just aren’t able to make her change directions.