Fix a small circle to the rim of a larger one and turn both, following a point on the smallest. Ancient astronomers used these epicycles to predict the wandering of the planets in the night sky. Centuries later, Joseph Fourier showed why they work so well: almost any repeating shape can be built by adding together circular motions of different sizes and speeds.

Four-Leaf Clover. Four leaves, each traced by the same chain of turning circles.