Straight from the 《木兰诗》 (the Ballad of Mulan): 雄兔脚扑朔，雌兔眼迷离，双兔傍地走，安能辨我是雄雌 - when male and female rabbits run side by side, who can tell them apart? The imagery of indistinguishable rabbits became a metaphor for the unsolvable.
culture
Because of the Mulan origin, Chinese readers often recall the 'hare on the run' image when encountering this idiom - a tiny echo of the Mulan tale lives inside every use.
