If you were to put a coin into an empty bottle and then insert a cork into the neck, how could you remove the coin without taking out the cork or breaking the bottle?
Push the cork into the bottle and shake the coin out.
A man came to visit at a convent while the superior mother was out of town. He left before she returned, and was careful to leave nothing behind. The nuns said nothing about his visit, so how did the superior mother figure out that a man had been there?