The lilac chaser is a visual illusion, also known as the Pac-Man illusion. It consists of 12 lilac, blurred discs arranged in a circle, around a small black, central cross on a grey background. One of the discs disappears briefly, then the next, and the next, and so on, in a clockwise direction. When one stares at the cross for at least 30 seconds, one sees three illusionsA gap running around the circle of lilac discs; A green disc running around the circle of lilac discs in place of the gap; and The green disc running around on the grey background, with the lilac discs having disappeared in sequence.