Nautical in origin and from the early 19th century, show a leg means to get up frpm bed, to hurry or be alert. One version of its birth says that when the bos’n’s mate on sailing ships woke up the crew in the morning, he cried, “Show a leg, show a leg or stocking!” At that time , according to the story, women were allowed to be on board ship, ostensibly as sailors’ wives, and “a leg in a stocking put over the side of a hammock indicated that the occupant was a woman, who was allowed to remain until the men had cleared out.” A more prosaic and reasonable account says the bos’n cried, “Come on, all you sleepers! Hey! Show a leg and put a stocking on it.” Shake a leg, meaning “hurry,” may derive from this earlier phrase, for both are nautical expressions and no better explanation has been given.