Princess and the pea

A prince who lives in a castle are looking for a princess to marry. One evening a girl knocks on the castle gate, wet and cold, claiming to be a real princess. The queen at the castle wants to put the girl to a test to prove she is a real princess. The princess is offered to stay overnight in a bed of twenty mattresses with a pea underneath. Only if the girl is sensitive enough to notice the little pea she is a real princess..