This perk is obtained by getting an Insta-Kill and killing no zombies until after it expires, then the player should see a green mist emerge from their character, upon this mist there will also be the sound notifying you have got a Persistent Upgrade. The Red Insta-Kill lasts for half the duration of Insta-Kill, fifteen seconds, any zombie touching your character will be automatically killed. Killing zombies doing this only gives 50 points, this Persistent Upgrade is lost by getting hit by a zombie on Insta-Kill.