Playing with the Pulfrich effect: perceiving a two-dimensional image as three-dimensional.

Through the Pulfrich glasses, the shadow of the cube gains depth. The eye looking through the darkening grey filter receives less light. As a result, it sends nerve impulses slightly later than the uncovered eye.

A minimal time difference, yet enough for the brain to interpret the cube as three-dimensional. A phenomenon discovered by the German physicist Carl Pulfrich and named after him.