Jack Fosters starting trap
The Frost trap is Jack Fosters starting trap. It consists of some isicles hanging above the doorway and a tank of what appears to be liquid nitrogen that lets out freezing cold air onto the zombies. This freezing cold air that hits the zombies causes them to freeze for a short period of time. Frozen zombies are killed in one hit, because as soon as you hit them the ice shatters; killing the zombie.