For a persistent upgrade with a similar effect, see Persistent Upgrades#Insta-Kill_Pro. 

Explosive Touch (Referred to as "Overcharge" in the game files) is a power-up that appears in the Exo Zombies maps Carrier and Descent, replacing Hyper-Damage. It is represented by a star. While this power-up is active, Zombies will be instantly killed if they make contact with the player.