Does the black circle in the center of this image seem to widen as you look at it? If so, it’s not the image moving—it’s your eye! The black center of your eye is called the pupil. It dilates, or expands, when it’s dark so your eye can take in more light. This helps you see better in dim conditions. Scientists discovered that this image tricks most people’s eyes into thinking that it’s about to get dark. Their pupils widen, making the central dark spot appear as if it’s expanding too!