We used to play with those too,
I found that a magnifying glass in sunlight could set them off without touching them. Better: if you tear them so that the paper is long on one side and right up against the little round dot on the other, they fly. We used to launch them at each other from about a foot away. Completely harmless and good for an hour's laughs when you're nine years old.

Unfortunately a neighborhood kid discovered that if you dunked a whole roll of caps in gasoline and used the magnifying glass to set one of them off the entire thing burst into flame and shot bits of burning paper everywhere. He got caught and playing with magnifying lenses got banned.
( The Resident Loon Not a demographic. Do not measure., Fri 10 Aug 2012, 18:10, Reply)