There's a tiny hole in the bottom of the shaft of this fish hook. When a fish yanks on the hook, it discharges a 4mm centerfire cartridge and, hopefully, shoots the fish.

These unusual guns were produced in the late Nineteenth and early Twentieth Centuries. If you can find one, I wouldn't recommend using it, as doing so would almost certainly violate the second and fourth rules of gun safety.

Link | Photo: Wayne Driskill Miniatures