Jew's harp

musical instrument comprised of a metal frame which is held between the teeth and a metal tongue that makes a twanging sound when plucked

The Jew's harp, jaw harp, or mouth harp is thought to be one of the oldest musical instruments in the world; a musician apparently playing it can be seen in a Chinese drawing from the 3rd century BC [1]. It is also sometimes called a Jew's trump or juice harp, among other names, and has no particular connection with Judaism.
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Noun
1. a small lyre-shaped musical instrument that is placed between the teeth and played by twanging a wire tongue while changing the shape of the mouth cavity
(synonym) jews' harp, mouth bow
(hypernym) musical instrument, instrument

(n.)
The shackle for joining a chain cable to an anchor.
  

(n.)
An instrument of music, which, when placed between the teeth, gives, by means of a bent metal tongue struck by the finger, a sound which is modulated by the breath; -- called also Jew's-trump.
  

hand-sized instrument placed in front of the mouth; sound produced by blowing across, and simultaneously twanging, a flexible 'tongue' set into a frame; many types. Also known more recently as Jaws Harp.