In one episode of Fool Us, when Penn and Teller are performing a trick of their own at the end, Penn establishes that Teller (who is supposedly doing a card trick) has not really lost the card picked by a woman in the audience in the deck. Then he cuts the deck himself and asks her again if she is now satisfied the card is lost. When she responds yes, he shouts, "Wrong! No matter how nice I am to you, or how mean I pretend to be to this man here, my first allegiance in the world is to my partner!" Despite that this was all part of the act and the rest of the routine is about Penn bullying Teller to the point that Teller stabs him through the hand with a knife, that one line is clearly actually true and really sums up the level of trust involved in such a close, lasting professional relationship.
Another episode of Fool Us has a fifteen-year-old boy, Daniel Kramer, performing. Though he doesn't fool them, Penn's speech after his performance is pure warm fuzzies.