If there’s ever excuse to publish an optical illusion as cool as the “Rotating Snakes,” I’ll take it. This illusion was invented in 2003 by Akiyoshi Kitaoka of Ritsumeikan University in Japan, and ever since, Kitaoka and other scientists have been trying to figure out why it works. A new paper by Stephen Macknik at the Barrow Neurological Institute in Phoenix may have the answer.

As you’ll notice, the circles seem to rotate in response to where you look at the illusion. So Macknik and his colleagues tracked the movement of people’s eyes as they gazed at two of these wheels on a computer screen. Their subjects kept a finger pressed on a button, lifting it whenever they seemed to see