Can you, scientifically, describe the Flood?

The Flood is a parasitic virulent life form which is spread by infected carrier hosts. The Flood appears in three primary forms: Infection, Combat and Carrier forms, but also have more mysterious forms like the Brain form and the Juggernaut form. All of these have an attraction to any sentient lifeform and will try to attack/infect any they encounter. The lifecycle of the Flood begins at Infection form as a small, frail, gas-bloated creature that leaps upon a host and attempts to drive in three barbed tentacles (although the small spores that some Flood are seen to release are also used to infect, as 343 Guilty Spark explains over the din of The Library level in the first game). From here, the host is paralysed and loses consciousness. The infection form gores itself deep into its host, usually in the chest. For a while it plays with its new body, and over time it mutates it by changing hormones and replacing the host's nervous system with its own tentacles. The host is never fed, and is carelessly treated. Often limbs become infected and begin to rot. Vital organs are liquified and the neck is broken. The disused head of the victim eventually falls off. If the host is of suitable size eg. Human or Elite, long whip like tentacles emerge from the arms as weapons. If not of suitable size, then the next stage of mutation occurs early. The body becomes so bloated and rotten that it may no longer be used as a Combat form. Smaller Infection forms grow within the ball of flesh, as it swells with gas and juice. Eventually the Carrier form falls over (or simply gives up) and explodes. Roughly 4-9 infection forms are emitted and continue the cycle.

From the Wiki article (explains all