This phrase is taken from Hamlet. In the play-within-the-play scene, Hamlet remarks ironically that there is no need for King Claudius, his usurping uncle, to feel troubled by the plot, remarking: ‘let the galled jade wince, our withers are unwrung’. The withers are the bony ridge between the shoulders of a horse which is liable to be chafed by an ill-fitting saddle.