The magician shows the box empty to the audiences and with his glance it suddenly bursts into flames but the flames immediately vanish. (You can keep the flames as long as you wish). The magician then shows the box empty to the audiences again, and he makes a very big silk appear from the box. He passes the corners of the silk from the holes, which are seen on the sides of the box.
This action is clearly done infront of the audiences so they can see what is happening. Everybody sees that the silk has been passed from the holes, and instantaneously, with the magician's glance, both the silk and the box will be on fire, so the audiences see the burning of the silk but the fire again vanishes but the silk has not been damaged.