Leonard: I think what Penny meant is, the thought of you two in a mine is kind of funny-- it's like a cat riding a Roomba.
Howard: If they get scared, they'll have those hats with the lights on them, 'cause down there it's night-night all the time!
Bernadette: Maybe they could ride around in one of those mine carts that go,(squeakily): ee-oo-ee-oo-ee-oo.
Leonard: Yeah, it'll help them get away when they see a gh-gh-ghost...!