I read about this a few months back when I read that the UK was freaking out over this little thing called a WASP Knife. Apparently, this is a specialized knife that can inject pressurized CO2 gas into your target and create a small frozen ball. Said ball inflates (about to the size of a basketball) and then explodes, leaving quite a mess and probably killing whatever you stabbed. It’s supposed to be used mainly on sharks (and the possible bear or whatnot), but can be used on lots of other things. Hasn’t been used on a person yet, but it’s pretty dangerous.
FYI, this isn’t the first time something like this was invented. Back in the 70s, the Navy had a similar weapon, except it was a hollowed spear that could inject CO2. Was mostly used on sharks (not to kill them, but to get them to back off), but would occasionally kill them since it would inflate their bellies. Even caused their stomachs to come out their mouths…(not a pretty sight)
Here’s some links if you’re interested:
(Has a video demonstration on a watermelon.)