- last post: 01.01.0001 12:00 AM PDT
Alright, time to set the facts straight.
The flood is a omni-parasitic organism which takes over suitable hosts by tapping into the spinal chord and the host's central nervous system (CNS). Combat forms turn into a carrier form when it becomes too injured to continue it's duties. Grunts and Jackals are also turned into carrier forms, most likely due to the host's natural weakness. Hunters are not infected, either due to their lack of cognitive capability or some natural resilience.
So humans, elites, jackals, and grunts become carrier forms. However, in Halo we only see 1 type of carrier form: humans.
Sarge. Johnson was unable to be infected by the flood due to boron's syndrome, caused by exposure to high-yield plasma, which messed up the electrical impulses in his nervous system, so the flood couldn't possess him.
I reckon it would be quite cool if you could see people being taken over by the flood in Halo 2, so that when they become infected, they turn against you (if friendly), and if you leave them alone for long enough, they turn into a flood form.