CARNAC (Holding the envelope to his forehead): "Sis, Boom, Bah."
ED McMAHON (Reading the question): "What does it sound like when a sheep explodes?"
CARNAC (Reading the question): "What forms on your dippity in the morning?"
I always thought he was at his funniest when he reacted to jokes in his monologue that didn't go over well. His ad-libbed comebacks were simply the best.