The challenge is quite formidable if you spell it out explicitly: artists must look at a three-dimensional scene with their two-dimensional retinas and then generate a two-dimensional painting that appears three-dimensional to viewers who look at it with their two-dimensional retinas. - Margaret S. Livingstone
In order to keep liking Nick (as opposed to loving him which was completely non-negotiable) Alice sometimes had to look at him obliquely or with her eyes half closed or through a pin hole on a piece of cardboard. Straight on would burn her retinas. - Carol Anshow