(Lisa tries to teach Bart a method to clear his mind of distraction.)
Lisa: Bart, I have a riddle for you. What's the sound of one hand clapping?
Bart: Piece of cake.
(Bart opens and closes his right fist quickly, making a sound.)
Lisa: No, Bart. It's a 3000-year-old riddle with no answer. It's supposed to clear your mind of conscious thought.
Bart: No answer? Lisa, listen up.
(Bart quickly opens and closes his fist again.)