similarity: a Gestalt principle of organization holding that (other things being equal) parts of a stimulus field that are similar to each other tend to be perceived as belonging together as a unit
gestalt law of organization: a principle of Gestalt psychology that identifies factors leading to particular forms of perceptual organization
hirschsprung's disease: congenital condition in which the colon does not have the normal network of nerves; there is little urge to defecate so the feces accumulate and cause megacolon