Wow! You've just built a "Phenakistoscope" a machine which produces the illusion of movement. This machine was first built in 1831 by Dr. Joseph Antoine Plateau and Dr. Simon Rittrer.

How? When you look through the tiny slots on the Phenakistoscope you see one picture quickly followed by another. Your eye and brain remember the first picture and blend it with the next. This ability to blend pictures that are shown very quickly is known as "persistence of vision" and it's what makes the pictures in movies or on TV appear to move.

Wow! Again.  "Persistence of vision" is also what makes the animations on this web site appear to move!