  Mitchell Feigenbaum discovered an intriguing property of viewing images
through cylindrical mirrors or looking into water. Because the eye is a lens
with an opening of about 5mm, many different rays of reflected images reach the
eye, and need to be interpreted by the visual system. This has the surprising
effect that what one perceives depends on the orientation of the head, whether
it is tilted or not. I explain and illustrate this phenomenon on the example of
a human eye looking at a ruler immersed in water.
