The bassoon is an unusually long instrument, nearly four and a half feet in length. Since the tube of the instrument has a folded shape, it would reach almost twice that if extended to its full length. At the tip of the instrument is attached a fine metal tube known as a bocal. The bassoonist blows air into the double reed attached to the very end of the bocal. The bassoon is unusual among wind instruments as all ten fingers are used to play. The role of the thumb is particularly distinctive, and there are at least ten keys that can be operated using the thumb of the left hand.