Where did the expression shake a leg which means hurry up come from?

Answer 1

It comes from the American Civil War. The battles of the civil war were bloody and gruesome. Often after a bayonet charge, the dead and wounded would often end up in a tangled and bloody pile. When the fighting ended, the stretcher-bearers would come out to sort the dead from the wounded. One way they had to sort the bodies between the dead and those still living, was to lift a leg or an arm and jostle it, to see if they got a rise out of the body. As you can imagine having one's limbs shaken while already wounded was quite a painful experience, so a soldier learned to move or wave one of his arms or legs by himself to indicate to the stretcher-bearer that he was alive. After a time, the stretcher-bearers would first yell to the piles of bodies "shake a leg or arm" as they approached. After a time, the shortened "shake a leg" began to be used in any situation where one wanted to rouse someone to action.