I saw that bit live in Radio City. I got to participate in a card trick where several people from the audience sat in chairs in a row across the stage. The person on the right would select a card randomly and we'd pass it down the row so we'd all know what it was. Then this booming voice from somewhere unseen would announce what card it was no matter how carefully we had concealed it while passing. It was a few cards into the bit when i realized the person to my left was in fact Teller in disguise and he was speaking into a microphone in his sleeve. He let us find him out by being intentionally sloppy as this was the comedic element of the trick. I lolled.