A metal headcrab is engineered by the Combine. When a metal headcrab latches onto a host's head, the headcrab would make the host's skin, organs and bones turn into metal. The only way to kill a metal headcrab and a metal headcrab zombie is to shoot it with a shot gun. The metal headcrab zombie is twice as strong as a normal headcrab zombie. When the host is a zombie, they are still alive and aware of what's going on, and the host tries to scream, but the headcrab makes their screams turn into metal groans. They are also immune to manhacks and barnacles.