These 14th-century weapons took inspiration from another weapon, fire-birds, which were actual birds that were outfitted with small pouches of smoldering embers around their necks and released into enemy cities. The red-hot embers would either fall out or burn through the pouches and land on rooftops, starting massive building fires.
The problem with fire-birds was that the birds were alive and would fly not only into the defending city but also to the tents and siege works of the attackers, where they would burn down the camp and s**t on everything.
But seriously, birds are the worst.
The Chinese tried to get around this problem with devices that are detailed in the awesomely named Fire Dragon Manual. The Flying Crows were dummy birds constructed with bamboo frames and paper skin, and each one contained an explosive warhead. They were launched into the air via a rocket with a range of more than 1,000 feet. When one crashed into its target, be it a ship or some building in a besieged city, the warhead detonated. While this is a terrific idea, we have to question why the bird disguise is even necessary.
Hopefully it was a little less conspicuous than this picture would have us believe.