Make some really thick salt water. REALLY thick. soak a piece of thread in it somewhere between 45 and 60 minutes. take it out and let it dry. Now you are ready. Ask someone for a ring. Tie it to the end of the thread. Hold the string so its like a pendulum.

Now take a match and light the string down by the ring. The string will burn but the salt crystals can hold up a fairly light ring. An awesome effect.