The Tradition Today: The pinky swear or pinky promise is normally a practice confined to primary school playgrounds, where it is immensely serious business. In the vein of an Unbreakable Vow for the younger set, the two oath-takers link little fingers to signify the sealing of a promise that has been made. Where It Came From: Allegedly, this practice originated in Japan, specifically with a digit-detaching practice of the Japanese mafia, the Yakuza. The concept of purported origin is known as yubikiri (literally, finger-cutting), and apparently has its background in loyalty practices among the Yakuza wherein a little finger would be cut off as a result of dishonesty or betrayal. This cant really be proven, but it certainly adds a morbid spin to the whole affair. Regardless of the accuracy of the Japanese mob link, the pinky promise is not without its ominous origins in North America, either; appearing in 1860 in a book entitled Bartletts Dictionary of Americanisms, in which the practice was said to be accompanied by the following rhyme in America:
Pinky, pinky bow-bell, Whoever tells a lie Will sink down to the bad place And never rise up again.
Yikes. Innocent playground practice, violent mafia loyalty practice, or Satanic cult ritual? One can only guess.