Sheldon: Are you still mad about the sperm bank? Leonard: No! Sheldon: Do you want to hear an interesting thing about stairs? Leonard: Not really. Sheldon: If the height of a single step is off by as little as two millimeters most people will trip. Leonard: I don't careâ€”two millimeters?! That doesn't seem right. Sheldon: No, it's true! I did a series of experiments when I was twelve; my father broke his clavicle.