Ozark Jaws Harp
Jaws harp, or "Jews Harp" provides a base note which is unchanging, but harmonics can be changed by moving the cheeks in and out.
Consists of a piece of vibrating metal in a metal frame. Part of this is inserted into the mouth, and the vibrating piece sticks out and is twanged with a finger. The volume of the note can be varied by breathing in and out.