The magician shows a black metal tube to the audience. They can see right through it. Setting down the tube, the magician removes a candle from his table and lights it. There's no doubt about the fact that the candle is real. Slipping the tube on his forearm, the magician then calls attention to the fact that there is a small hole in the tube - though which the candle easily passes. It also just so happens that his arm is blocking the hole in the tube. No matter. The lit candle passes through the hole in the tube, and the magician's arm at the same time! The candle is moved back and forth as it passes through the arm. At the conclusion of the routine, the candle (and arm!) can be thoroughly examined. Extremely easy to do and completely safe.