Parallax

flat dots, until they move. turn them and guess the shape.

a still cloud of same-size dots is flat noise; turn it and a hidden 3D shape pops out from motion alone, then guess which

Every dot is the same size and the screen is flat, so a still cloud carries no depth at all. When it turns, near dots slide one way and far dots the other, and your visual system solves for the shape that would move like that. This is the kinetic depth effect (Wallach and O'Connell, 1953). Stop, and the shape is gone.

Concepts: depth, perception.

An interactive you play with one thumb, on Wundr.