"Teller almost never speaks while performing. There are exceptions such as when the audience is not aware of it; for example, he provided the voice of "Mofo the psychic gorilla" in their early Broadway show with the help of a radio microphone cupped in his hand. Teller's trademark silence originated during his youth, when he earned a living performing magic at college fraternity parties.[13] He found that if he maintained silence throughout his act, spectators refrained from throwing beer and heckling him and focused more on his performance.[14]"

-Wikipedia on Teller