Wasp knife is a trade name for a large knife that contains a cylinder of compressed gas in the hilt. When stabbing a subject, about one cubic foot (or 28 litres) of gas stored at 800 psi is rapidly injected deep into the wound site.
The injected gas causes much more damage than a single knife wound, both from the displacement of internal organs and from the freezing effect of the free expansion of the gas.
One well-placed hit can easily kill or immobilize a large shark. When used underwater, the freezing effect helps to keep the animal from bleeding profusely, while the injected gas causes the animal to float to the surface. This can be very helpful in defending against aggressive sharks, while avoiding the blood release that can trigger a feeding frenzy in a group of sharks.
The Wasp knife was notably featured as a murder weapon in the Season 7 episode of CSI: NY, Identity Crisis; the Season 8 episode of NCIS, False Witness; the Season 12 episode of Law & Order: Special Victims Unit, Bang; and the Patricia Cornwell novels Red Mist and Port Mortuary, and in James Rollins' "The Doomsday Key".