Imagine opening a bag of chips, only to find Santa Claus looking back at you. Or turning a corner to see a building smiling at you. Humans see faces in all kinds of mundane objects, but these faces aren’t real— they're illusions due to a phenomenon known as face pareidolia. So why exactly does this happen, and how far does this distortion go? Susan G. Wardle explores why we see illusory faces. Lesson by Susan G. Wardle, directed by Oksana Kurmaz.