Insta-Kill

Insta-Kill, short for Instant Kill, is a power-up available in all Nazi Zombies maps (not including Dead Ops Arcade).

Overview
Insta-Kill is a power-up which makes every zombies die with only 1 shot or 1 knife or any other form of killing a zombie instantly, however inst-kill only lasts for 30 seconds.

It is also good on high waves because the zombies are easyer to kill and it's a good way to save ammo as you can knife the zombies as if it was round 1.