Here's an abstract from a medical journal that discusses a spring knife fatality. While I've always considered the "Spetznaz" knife to be gimmicky, at distances up to a meter, it does have the potential to be lethal.
Joel
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Fatal brain injury caused by the free-flying blade of a knife - case report and evaluation of the unusual weapon.
Hirt M, Karger B.
Int J Legal Med. 1999;112(5):313-4.
Institute of Forensic Medicine, Masaryk University Brno, Czech Republic.
A man suffered a fatal injury from a self-inflicted accident while handling a special type of knife. A spring in the shaft of the knife accelerated the blade, which perforated the orbital cavity and the frontal lobe at the right side. Death was due to central disregulation. The initial velocity of the blade was measured to be 15 m/s. In a total of 20 experimental shots to a fresh pig cadaver, the blade always penetrated the skin and 5-10 cm of soft tissue as long as the distance did not exceed 1 m. Thin layers of bone were also perforated. The free flight of the blade did not remain stable if the distance was more than 1 m, which resulted in superficial wounds only. So this unusual construction resembling a knife can be considered an effective combat weapon for close range fighting instead of a tool.
