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The magician shows an elegant box with two holes on its sides; he puts a silk inside the box, running it through the two holes. Suddenly the box bursts into flames, but the silk doesn't burn down... instead, it is pulled from one side to the other of the box, staying undamaged!
Finally, the fire ends and the silk is shown intact. The box is once more shown on its inside and it doesn't have any gimmick.