The expression "Say cheese" came about from a combination of things in the mid-20th century: a relaxation of mores surrounding photography, an improvement in oral hygiene, and advancements in photography (largely from Kodak) that made cameras much less expensive. Prior to that, smiling was not considered appropriate among those who could afford to have their photographs taken. Consequently, photographers in the UK often advised their subjects during the mid-19th century to say... WHAT? This food word apparently helped encourage a tightening of the lips.