Jack-in-the-box

A jack-in-the-box is a children's toy that outwardly consists of a box with a crank. When the crank is turned, it plays a melody, often "Pop Goes the Weasel". At the end of the tune there is a "surprise": the lid pops open and a figure, usually a clown or jester, pops out of the box. Some jack-in-the-boxes open at random times when cranked, making the startle even more effective.