- last post: 01.01.0001 12:00 AM PDT
As for the other flood forms, they are separate matters. Combat forms for instance, aren't really killed as such. An infection form after having neutralized a potential victim enters it (usually in the chest cavity when the prey is a humanoid), and controls its motions from there, and presumably in some way feeds off the host. To neutralize a combat form, you can either directly "go for the brain" and kill the infection form, or cause so much damage to the host that it can't sustain the infection form any longer, or at least so that it gets too badly damaged for the infection form to control.
Upon infection, it seems that the infection form erases most (if not all) of the unfortunate victim's thoughts and emotions, and replaces it with the endless, parasitic hunger of the flood. Eventually the victim's physical structure is also changed, in a way that seems to lead to greatly increased strength and durability, but also wears most host bodies down very quickly, as they are rarely intended for the kind of physical punishment the infection forms subject them to.
The final stage of the flood life cycle seems to be the carrier form, although I guess it's hitherto unknown whether a carrier form can be created directly from a host, or if a combat form must be created as a middle step, or if both ways work. While combat forms are obviously created to protect the rest of the flood colony and to subdue potential victims; the sole purpose of the carrier form appears to be evolving new infection forms in it's ballooning thorax, and "giving birth" to them through a rather powerful explosion which can be used in an offensive manner.