Flickering circles with a light and dark side at their edge (also known as Craik-O’Brien-Cornsweet circles) appear to wander. Even though these circles are not moving (only flickering), the shapes seem to drift whenever you do not look directly at the circles. Even if you put a line right next to a circle, the shape will still seem to move, but never across the line. The more circles you add, the more motion you see!
Christopher Blair, Lars Strother, and Gideon Caplovitz: “The Wandering Circles”