A Pen created at CodePen.io. You can find this one at http://codepen.io/godds/pen/qjLdp.

 This illusion, where the movement of two points along a square and circle appear to interfere with each others' motion, was created by Maarten Wijntjes, Robert Volcic & Tomas Knapen from Utrecht University.  It was a finalist in the 2008 Illusion of the Year contest.
