Video courtesy R. A. Wilson, manualist

Manualism is the little-known art of playing music by squeezing air through the hands. Because the sound produced has a distinctly flatulent tone, such music is usually presented as a form of musical comedy or parody. The musical performer is called manualist, who may perform a cappella or with instrumental accompaniment.
Playing recognizable tunes by squeezing the hands together is extremely difficult, and it takes many years of practice to master the art. Some manualists practice for as much as 30 years before finally reaching a presentable level of proficiency. In 2006, only a handful of manualists perform publicly. Source: Wikipedia.org