Pull finger/pull your finger out

Pull finger or pull one’s finger out means to stop messing about, or stop standing by idly, and get a move on with whatever task is at hand. Some sources ascribe a military or nautical origin, about placing a small amount of gunpowder in the ignition hole of a ship's cannon or artillery piece, and holding the gunpowder in place with one's finger. Just before firing the cannon, the order would be given to pull the finger out. This theory is most unlikely given that the expression is first cited from the early 20th century. Other sources, including Eric Partridge, maintain it is RAF slang from around 1930, deriving from a slightly earlier and somewhat vulgar expression, namely, to sit/stand around idly with one's finger up one's arse (or ass) depending on which side of the Atlantic one is from. This explanation is probably nearer the mark, because essentially the expression is designed to rouse someone from just such an idle state. Truth be known, the origin remains obscure and no one knows for sure.