Page 128 - Gibson W.B. "The complete guide to knots"

,
The Appearing Knot

Take a handkerchief and hold it by
one corner. Shake it two or three
times and suddenly a knot appears in
the hanging corner of the
handkerchief.
Here is how it is done: Start with a
handkerchief with one corner tied in
a knot. Hold it as shown in figure 1
with corner A hanging down. The
corner with a knot in it (corner B) is
concealed in the right hand.
Lift up corner A with the left hand,
so that both corners are held in the
right hand. Give the handkerchief a
quick shake and let corner A fall
again. Repeat this two or three times,
and act disappointed when no knot
appears.
The last time you take up corner A,
so that you have both corners in the
right hand (fig. 2), hold on to corner
A when you shake the handkerchief,
and let corner B fall instead. In other
words, exchange the corners (fig. 3).
Those watching the trick think it is
the same corner all the time.