Who hasn't, at some point or another, made a pinky swear with a best friend or a child? The pinky swear is the highest of all promises, an unbreakable oath -- and, in fact, what you're saying with this oath is that if you break it, the wronged party may cut off your pinky. The gist of the custom (if not the bloody follow-through) is a recent immigrant to the United States, having originated with the Japanese mafia, or Yakuza.

The Japanese roots of the pinky swear are evident in its common use in anime films, where it is known as yubikiri or "finger cut off."