On Yom Kippur we read from the Talmud tractate Yoma, the section dealing with Yom Kippur in the Beit HaMikdash, the Holy Temple in Jerusalem. Chapter 3 mentions Hogros ben Levi, one of the Levites in charge of music in the Holy Temple:

"Hogros b. Levi - We have learned in a Boraitha: When he had to render his voice melodious, he placed his thumb in his mouth, and the index in his mustache. When all his fellow-priests heard his voice, they bent to the ground (from ecstasy)." Other translations state that he put his thumb under his tongue to create a most beautiful melody.  

For more information visit:
* http://www.jewishvirtuallibrary.org/jsource/Talmud/yomatoc.html
* http://www.sacred-texts.com/jud/t03/yom08.htm