The Jaw Harp, commonly referred to as jew harp, jew's harp or mouth harp, is one of the most interesting musical instruments around. It has a small, key-shaped frame with a tongue inside that is used to generate sound. Historically they have been constructed of everything from wood to bamboo to metal. Today however, they are almost exclusively made with metal. The Jaw Harp is thought to be the oldest instrument in the world, and is popular on just about every corner of the globe.