(Note: This exhibit is shown from the rear to show the rotating cube as well as its shadow.)
A 3-dimensional skeleton of a shape, in this case a cube, is suspended in behind a translucent screen. A small motor rotates the shape continually in one direction. When a strong light is projected through the object onto the screen, a viewer on the opposite side of the screen will perceive a shadow of the rotating object. However, there will not be enough visual clues for the viewer to determine which direction the object is rotating, so sometimes it will be seen as going one direction and other times a different direction.
This exhibit illustrates how the brain will take visual clues and attempt to fit them into a logical scenario. If clues are missing, the brain may make multiple interpretations of the same image.