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).
[Illustration]
Fig. 4.