Gun shoots gas

Hi, hello there, mind if I stab you and then shoot compressed gas into causing you to explode? Well, it doesn't matter, i'm gunna do it anyways. This wasp knife is a pretty cool idea, and although using it on watermelons is not its primary function, the video is still kinda cool.

Here's the link:
http://gizmodo.com/5027010/wasp-knife-will-freeze-and-blow-up-your-organs

Of course, it makes me wonder, if you are going to make a knife shoot stuff, wouldn't you be better off just making it shoot bullets? Thus the inspiration for the new poll :P