This is a 3D Sumo Wrestler paper craft that uses the hollow-mask illusion. When you look at it from different angles, it seems like the head is moving.

Why does the Sumo Wrestler’s head appear to move on its own? Normally, faces stick out, right? But this Sumo Wrestler’s face is hollow—shaped like a bowl. Our brains are very good at recognizing faces. When the brain sees a hollow face, it gets confused because it expects faces to stick out. This confusion creates the illusion that the head is moving.

If you want to experience the hollow-mask illusion yourself, press the "Display PDF" button below to open a printable PDF file. Try making it and playing with it! If the Sumo Wrestler’s head doesn’t seem to move, try looking at it with one eye or through a camera lens—this makes the illusion easier to see.