Contour rivalry

Contour rivalry is an artistic technique used to create multiple possible visual interpretations of an image. An image may be viewed as depicting one thing when viewed in a certain way; but if the image is flipped or turned, the same lines that formed the previous image now make up an entirely new design.
This technique was widely practiced by the artists of the Chavín culture of the central Andes about two thousand years ago. An example of this technique from the Chavín is the Raimondi Stela.