Holding a piece of rope, the magician places the ends of the rope into his hands and closes his fingers around the ends. The magician shakes the rope slightly, says a magic word, blows on his hands and drops one end of the rope. Magic! The end has a knot in it!
One long piece rope
The rope already has a knot in one end... Tie a knot in one end of the rope. Hide this end with the knot in your hand and bring the other end of the rope up next to it. Shake your hand as if you're trying to knot it. Drop the end with the knot and it looks like you have tied a knot in the rope using one hand.