The xomus is a jaw harp, also known as a Jew's harp. The metal xomus used in Tuvan music is called the demir-xomus. The instrument consists of a flexible metal tongue attached to a frame. The frame is held against the performer's teeth, and the metal tongue is plucked with the finger to produce a note. The xomus is a one-pitch instrument, but the player, by changing the shape of his mouth and the flow of air, creates melodies by emphasizing various overtones. Ayan Shirizhik is pictured playing the xomus.

Folktale about the demir-xomus
Hear Ayan Shirizhik play the xomus [00:43] 
Hear Kongar-ool Ondar play the xomus [01:03] 
Watch Ayan Shirizhik play the xomus [00:15] 
Xomus (Jew's Harp) on Wikipedia