Pop Pop Snappers (aka snap-its, poppers, poppies, pop-its, snappers, snap'n pops, devil bangs, rio snappers, or bang snaps) are made with a cigarette paper rolled and twisted into the shape of a roughly spherical teardrop with a tail.
The teardrop is loaded with about 0.18 gram of small gravel or coarse sand coated with 0.0008 gram of silver fulminate, Ag₂(CNO)₂.
When the device is thrown against a hard surface, friction between the granules sets off the silver -fulminate with a quick bang.
The explosion generates little flame and almost no gas, as compared with toy caps, so that the granules are not widely scattered. Except for the paper wrap, they are nonflammable. They are safe in storage and shipment.
They are not set off by heating to 75°C (167°F) but will detonate if exposed to a flame. Even when detonated in the hand, it causes no burn, tingle, or damage.
For more info, refer to Chymist.com - Katz, David A. "Chemistry in the Toy Store". 6th ed, 2002.