Since the video appears to cause some confusion and to provoke the mentally handicapped to post idiotic comments, I guess I have to write a more detalied description for the sake of clarification.
As the more intelligent viewers figured out, this is not a ballistic knife which launches a spring-loaded blade, which should be obvious, since the knife is held with the blade facing the shooter. Instead, the knife fires a silent special-purpose 7.62mm cartridge.
Currently, there are two versions of the knife, the NRS and the NRS-2. NRS stands for "nozh razvedchika strelyayushiy" and translates literally as "scout's shooting knife". The NRS has a clip-point blade and fires the 7.62x38 mm SP-3 cartridge which, in terms of muzzle energy, is comparable to the .25 ACP. The NRS-2 is a spear-point design and uses the more advanced 7.62x42 mm SP-4 round (comparable to the .32 ACP).
Due to the cartridge's unique design, the knife (or any other weapon chambered for the same round) produces almost no noise or fumes. The bullet is pushed out of the case by a piston, which, at the peak of its extension, locks the case mouth, thus trapping the gases inside and eliminating the muzzle crack. So in the end what we have is an extremely silent weapon with a muzzle energy of 90 J for the SP-3 round or 200 J in the SP-4 chambering, which is more than enough to kill at ranges of up to 20 m.
Here's some additional reading with pictures:

NRS-2 knife:
[ Ссылка ]

Special purpose small arms ammunition of USSR and Russia:
[ Ссылка ]

Btw, japanigro's comment that I replied to was:
"lololol that wouldn't even kill a cat, you might as well be using a pea shooter."

He deleted it for some reason.

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