Two red hearts are presented below on a blue background. One of the hearts is “blurry” and the other is not. As you move your eyes back and forth between them, the blurry heart appears to wobble (as if it were unstable) while the solid red heart does not.
This illusion was presented by Kohske Takahashi, Ryosuke Niimi & Katsumi Watanabe from the University of Tokyo (Japan) in 2010. It was also selected as a finalist in the 2010 Best Illusion of the Year contest.