A KNOT THAT CANNOT BE DRAWN TIGHT
Tie a single over-hand knot in a handkerchief, and holding it in your left hand, give one end to some one, telling him to pull at a given signal. As he is about to do so, slip your left thumb underneath and, letting go the end hanging over your left hand, allow the handkerchief to run between your thumb and forefinger, when it will come out without any knot ([Fig. 4]).
Fig. 4.