There are so many crazy fun things you can do with fire, this is probably one of the most tame. But it's got flame, so it's still cool. This video will show you how you can squeeze the peels of citrus fruits onto a candle (or large flame for increased fun) and the acid will cause the flame to burn larger and brighter for a flash. Experiment with different peels and flame sources for extended fun. Grapefruit work fantastically.