It's a little like the visual pun in Charles Allan Gilbert's All is Vanity, or those picture book games, which one is different. You know, where you have to look closely at a set of pictures of chickens or Alexander Hamilton to finally see that one of the chickens has a third toe or Hamilton has a spot on his brow. It's a very subjective exercise; the eye sees what it wants to see, that's the nature of cognitive blind spots.
Problems, puzzles and sometimes murder.
