“Thus A is seen as a white triangle lying atop of triangle B. In reality, of course, nothing is lying on top of anything else. Instead your computer monitor is showing you a pattern of pixels that you interpret as a figure with depth.

“So remember, powerful and compelling illusions can be created with the simplest of shapes. These illusions arise because our visual system is trying to solve an unsolvable problem. Usually it does a great job, but we can trick it with just the right illusions.”