Check this monster out.
The WASP Injector Knife has a hidden CO2 canister in the handle. If you get attacked by a shark, you can stab the shark (or other large attacker). When you click the button, it discharges the canister with a blast of 850 psi of gas through a small tube in the knife blade directly into the body of your fishy attacker.
The description from the website tells the full story:
This weapon injects a frozen ball of compressed gas approximately the size of a basketball at 850psi nearly instantly. The effects of this injection will drop many of the world's largest land predators. The effects of the compressed gas not only cause over-inflation during ascent when used underwater, but also freezes all tissues and organs surrounding the point of injection on land or at sea. When used underwater, the injected gas carries the predator to the surface BEFORE blood is released into the water. Thus giving the diver added protection by diverting other potential predators to the surface.
No word of when it will be available on the market.
Not your average knife indeed.
New rule: don't bring this knife on any of my courses. I don't want it accidentally discharging off in my leg...
More info: waspknife.com [Via: Boing Boing Gadgets]