The hmongs are a predominant ethnic group in Southern China, Northern Laos and Vietnam. they all come from Guizhou province (China) where they are called Miao. The ones who left China in the 19th century have re-defined various cultural identities since then, but musically speaking, the mouth organ remains their main distinctive instrument.
Hmong from Vietnam have a specific way of singing called "hunga" and all instruments they use like the "chungja" (jew's harp) or the "khen/keng" (mouth organ) tend to imitate this singing.
The "chungja" is a small jew's harp with one blade made of copper used by lovers to talk to each others whereas the "keng" is rather used by musicians dancing while playing to seduce a woman.