What Shall We Do Now? — Dorothy Canfield

" ...]whistle is moving in the way that the slipper moves in "Hunt the Slipper." The object of the player in the middle is to discover the person who blew the whistle last. Meanwhile some one skilfully fixes another whistle on a string to the player's back, and that is the whistle which is really blown. As it must always be behind him when it is blown, nothing but the twitching of the string is likely to help him to discover the blower (and the trick); and in a small ...]."