Sneaking bombs into a castle or village would be a wonderful way to surprise and defeat one's enemies. We do that with aerial bombing these days, but in the Middle Ages, it took thinking outside the box. A 15th-century German book called Feuerwerkbuch (Firework Book) included plans for sending bombs inside fortification by means of cats. The quote in the book is from Franz Helm in 1530.
If you would like to get at a town or castle, seek to obtain a cat from that place. And bind the sack to the back of the cat, ignite it, let it glow well, and thereafter let the cat go, so it runs to the nearest castle or town, and out of fear it thinks to hide itself where it ends up in barn hay or straw it will be ignited.
The illustration leads us to believe that bird bombs were also considered, but that would be an iffy way to deliver bombs, since there's a possibility they would explode in mid-air. The lack of documentation of cat bombs in the historical record gives us no reason to believe that this method was ever successful, nor whether it was even attempted. Attempts that failed were understandably less likely to be recorded. -via Cracked