Two Eyes provides a physical illustration of the "stereo rule" with two giant eyeballs. Each eyeball has a cornea, a lens and a retina. Two boxes in front of the eyes have large letters painted on them--one contains a red F and the other a green P. Images of the F and P form on the back (retinas) of the eyeballs. Visitors can observe how these images are upside-down, and different distances apart in each eye. Placement of these images on the retina is one of the clues the brain uses to determine depth. You can move the letters and see how these movements affect the placement of the images on the eyeballs.