Gonome

The Gonome  is the a further stage in the mutation of a Headcrab Zombie. The Gonome appears only in Half-Life: Opposing Force.

Creation
A standard Headcrab Zombie is created when a normal Headcrab attaches itself to a viable Human host by latching onto the head, and using its 'beak' to open the skull and expose the victim's brain. The Headcrab causes mutations in the host, such as rapid growth of finger nails, increased physical strength and increased resistance to harm. Another aspect of the mutating is a rip in the torso spanning from the neck to the waist. Whether this injury is due to the parasite devouring the flesh, or by neglect is unknown.

After a few hours, provided the host survive, the mutations become more drastic. The host becomes more muscular, and their claws become longer still. The tear chest swells and becomes a vestigial mouth, from which a corrosive saliva can be pulled. The acid is derived either as part of the mutation or generated by the host's stomach. Across the shoulders, several underdeveloped reptilian eyes begin to emerge.