This is another great example of how easily your eyes can fool you!
The circles appear to be slightly rotating, but in fact, they are not moving at all. It is the
shadows that move around it that give the illusion.
You can be fooled in everyday life by this simple process. Sunlight, reflection, blocked light or moving light can change the shadows of
objects of any kind to give the illusion they are moving. You might have seen a stick and though it was a snake
because as your angle and perspective changed, the shadows changed.