Michael caught a remarkable show on National Geographic the other day, featuring some of the most interesting optical illusions of our time. Most of them we have already featured on this site. One of the featured illusions that made him scratch his head were the spinning balls you can see in this animation below. This is how it works: both of the outer rims (made from spinning balls) rotate in counter-clockwise direction. But if you try and focus on one of the central dots (i.e. yellow one), the outer rim of another will seem to spin in opposite direction! This works vice-versa. To put it short – concentrating on the yellow ball will make it seem that the balls on the left are turning in opposite direction, while in fact they aren’t! Strange isn’t it?