: Okay, so here's something I've been thinking about. I was going to give this
: a little more thought/do some more research, but opening this up to
: other's input couldn't hurt.

Half-baked idea=fewer people agree+plenty of room to argue=more replies
Well-supported idea=more people agree+less room to argue=dead thread

That's the theory I'm working under, at least.

: We already have a classification system for the Flood's developmental stages:
: Feral - they communicate via pheromones and have the instinct to harvest
: enough calcium to establish a viable Gravemind.
: Coordinated - at this point, they are controlled by the Gravemind that was
: created in the first stage.
: Interstellar - the Flood take control of space-faring technology which they
: use to consume the local star system. Subsequently, they spread throughout
: the galaxy to infect more hosts.

I think this would have held true for the unstoppable-blitzkrieg-from-hell Flood that the Forerunner encountered, but might not hold true for nascent invasions. If the Flood's goal is to establish a foothold in a galaxy, it makes sense that they might instinctively seek out means of interstellar travel before a Gravemind is even formed. As near as I can tell, this happened on the Infinite Succor.

: Intergalactic - a theoretical stage in which the Flood utilizes all
: captured technology to depart to uninfected galaxies to further replicate.

Actually, they hibernate out in Darkspace for about 50,000 years before returning via the...
Wait, wrong universe. Sorry.

: And each one of these Proto-Graveminds has had subtle differences in their
: appearance and/or mannerisms.

Naturally.

: The Keyes terminal from Anniversary added two new elements to the mix. One,
: we can hear the Gravemind communicating directly with Keyes through
: "thoughts". Internal communication direct from the Gravemind
: intelligence that, presumably, could not be heard externally.

How does telepathy work?

Ok, this is probably where a neurologist should come in and tell me I'm totally off-base, but there's a bunch of interesting mechanisms it could use.
Maybe the Flood was causing auditory hallucinations, and Keyes might have 'heard' the voice just like he would hear one of his officers talking to him. If the Flood tinkered with his immediate short-term memory he might have remembered being spoken to seconds before, even though... um... I guess whether the Flood would have spoken to him or not is a philosophical question.
Maybe direct thought-to-thought communication doesn't feel like 'hearing' a voice, so much as "Oh God, did I just think that?"

: Second, in
: the terminal when Keyes is remembering the Flood attack (bottom image), he
: appears to be ordering his men to retreat from a large, Proto-Gravemind
: like form, which displays quite a lot of movement. It almost appears as if
: this massive Proto-Gravemind is chasing after the marines, which goes
: against nearly everything we understand about Proto-Graveminds (save some
: stylization in stories such as The Last Voyage of the Infinite Succor ).

Back on the HWF, we forumites had a huge "How to Implement the Flood" thread, where we theorized how a multiplayer Flood faction might work. One of the working theories was that there was a stage between using infected hosts and pure forms, where broken hosts and discarded biomass would be glued together with liberal doses of the Flood Super Cell. So, that's what the Juggernaut would have been.

Thinking back upon it, the Flood could probably get pretty surgical. Muscles could be removed from hosts and grafted onto bioceramic bones, weaves of organic hyperfiber could be woven through tissue to improve endurance and shear strength, and pieces of armor from Marines, Elites and vehicles could be inserted beneath the epidermis.

Over time, the body would be entirely consumed by the Flood Super Cell, transforming the Amalgamation into a Pure Form. And the production of the Flood Super Cell in hidden enclaves (Crucibles?) would reach a point where hosts could be economically converted into the FSC wholesale.

*Only after re-reading this did I remember that hyperfiber is fictional. If you ever get the chance, pick up Marrow by Robert Reed.

: Lastly, the Proto-Gravemind from Halo Wars. This thing has always been a
: black sheep to me. It displays abilities that thus far only Coordinated
: Flood have demonstrated (the formation of infection pods, the massive
: spread of Flood biomatter, including complex tentacles and portas),
: specifically in Halo 3. However, it's been stated many times that this is
: indeed a Feral Flood outbreak, and that the various creatures presented
: are merely forms of infected wildlife native to the Shield World.
: Disregarding how interesting it is to consider the capabilities of the
: original infected creatures when compared to other Flood combat forms,
: this places the Proto-Gravemind at a certain point in its path to becoming
: a Gravemind.

OK, so, where did the Flood come from?
I know the answer is "Ensemble needed something to spice up the middle act", but I want to be Watsonian about this.
We know that the Halo Array kills almost all of the Flood: Offensive Bias still had to destroy the remains of the Flood Fleet after the Array was activated. Perhaps some form of the Flood Super Cell is resilient, perhaps there is a form that is immune (the powder?).

The powder... Oh.
The Forerunner didn't have any samples of it, because the Near-Humans destroyed their stocks.
So, perhaps the Flood wasn't repelled from the Femto-Dyson Shell because of an overwhelming assault that failed to get past the surface, but because a strange organic molecule arrived unnoticed on a meteoroid. Noticed, but given scant attention as a new strain of soil bacteria began producing it as a waste product. Analyzed as it became omnipresent in the biosphere, its mutagenic properties cataloged but misunderstood.

The time between the emergence of the first Flood-like properties and the mass conversion of thirty percent of the FDS's flora into virulent spores was a matter of hours. Defense measures would have been taken immediately. Doubtlessly, the FDS was already hermetically sealed, but more systems would have come online to prevent active penetration. Afterward, the ancilla in charge of the station had plenty of avenues of attack, none of them effective.

The best way to contain the outbreak would have been to destroy all biomass on the surface. Waste heat from the starforge at the center of the FDS would have been vented to the surface, and hard radiation was focused through lenses of exotic matter. Across wide swaths of the station's surface, organisms would have vaporized into plasma and mono-atomic gasses, or been disintegrated within torrents of ionizing radiation. But the fallout and backwash was deadly. For every kilometer of life erased, two more kilometers were merely extinguished. And immediately reincarnated.

Records show that explosively shedding the atmosphere and geological layers of the FDS was considered, and rejected. The energy required to remove it all from the Femto-Dyson Shell's gravity well was trivial, particularly since the ancilla controlled the machinery that generated the gravity. The reasons for not following up on this plan are unknown, but possibly linked to the uncertainty of creating more Flood-infested meteoroids, carried away on the solar wind.

Experiments showed that Flood activity was impeded by low temperatures, and the biological machinery within the Flood Super Cell ceased to function at seven point four nine degrees Kelvin. By powering down select power sources and obviating the need for the waste heat conduits, the ancilla could have frozen the Flood to a state of relative inertness. Eventually.
The station had been placed far from its sun, where waste heat would nurture a planet-wide garden. But there was no life left that needed the heat, and the Flood fends for itself. By the point where fifty percent of the remaining biomass was converted, spore cloud activity in the upper atmosphere had created an incredibly well-managed greenhouse effect.

At any point, the floodtides could have been stemmed. The FDS contained a fleet of warships fabricated late in the war, held in reserve for lack of crews to fly them. A handful of them could have been activated and shunted through slipspace to the outside of the station. Were the generated gravity to be increased a hundredfold, the warships could have fired their weapons until the geological strata were glass and the atmosphere a hot, shallow ocean.
Alternatively, a solar shield could have been erected, proving the Flood's efforts to be in vain. A hundred years, a thousand years, and the fleet could have been deployed to scour the ice and rock from the station. The rubble would be shielded in Forerunner metal and fired into the sun, or perhaps dropped into one of the dark singularities within a few light years of the system.

But the ancilla was negligent. Once a stalemate was achieved, it began automating the station's systems. Its fear of the Logic Plague was more acute than its sense of duty, and it soon began preparations for dormancy. Powered down, disassembled, to be made whole again when the situation improved. It would sleep for a long time.

...
... I just fanfictioned again, didn't I?

: Combining all of these, I started working on the following classification
: systems. First of all, a classification system specifically for initial
: outbreaks of the Flood. Each outbreak would be categorized by the Flood's
: introduction to a new area. For example, the outbreak on Alpha Halo would
: have started with the Covenant unlocking the weapons cache and discovering
: that it's not what they thought it would be. That would have then
: continued as the Flood were introduced into new systems on the ring, the
: individual outbreaks becoming part of the overall collective outbreak.
: When the Flood reached the Infinite Succor, that would have been another
: outbreak, even though it was part of the larger outbreak at Installation
: 04. Same with The Mona Lisa. Etc.

: So, I thought it could be broken down like this: Type 0
: If an outbreak occurs from inactive Flood biomatter, e.g. Cryptum. I
: classified this as Type 0 because it is not the "standard" or
: "intended" means of conveyance. The powder was merely a means to
: let the infection develop to the point where it reached its biological
: "standard".

: Type 3
: Direct assimilation into Gravemind or Proto-Gravemind – The Mona Lisa. This
: would be where the Flood are at a point of critical mass where they no
: longer need to convert hosts into combat forms, they can simply drag them
: off and add them to the growing Gravemind. No infection would occur, all
: possible hosts in the area would just be subdued and transported. Still
: not sure of this Type, I think an alternative Type 3 should be considered.

I used to think that Graveminds and Proto-Graveminds could rip memories and knowledge out of any infected host, but the Flood on the Mona Lisa dragged the pilot all the way down to the Proto-Gravemind to assimilate her.

Perhaps the issue is bandwidth? Searching a host's mind takes more bandwidth on the organic ansible than issuing orders or receiving immediate sensory data? Of course, the computational matter in an infection form is probably up to the task of taking apart a sentient brain and hunting down data. But perhaps the infection forms are limited, because our way of thinking is so alien to them? Perhaps searches and cataloging done by infection forms is limited, slow, inefficient...

Wait a sec. Graveminds are Google, infection forms are Yahoo?

: The two problems we run into are these: 1) The Proto-Gravemind from The
: Last Voyage of the Infinite Succor goes from having just begun its
: development to full communication in a very short time frame.

My guess: The Flood were in a hurry.

I also humbly submit the possibility that multiple Proto-Graveminds in a system can reinforce each other. The Proto-Gravemind on the Infinite Succor may have been nurtured and had its growth accelerated by Proto-Graveminds on the surface who saw the ship as their best chance out of the Soell system.

: 2) The Proto-Gravemind we encounter on the Flood-Controlled Shield World in
: Halo Wars is massive, appearing to be closer in size to the Gravemind from
: Halo 2 than the Proto-Gravemind from Halo 1. It also shows signs of
: growing through a vast majority of the Forerunner installation. Yet it displays no
: signs of external communication.

You mean besides spoofing Ander's plot device beacon?

Anyhow, according to a Q&A I read a while back, the Flood were introduced to the interior of the Femto-Dyson Shell when the Spirit of Fire was drawn through the quarantine system.
Which, to be honest, sucks as an explanation.

: This may be explained by the fact that, prior to the Covenant and Spirit of
: Fire's arrival at the Shield World, the Flood did not have access to any
: life forms of significant sentience. As a result, they could expand
: physically through the consumption of more lifeforms over hundreds or
: thousands of years, but not mentally, leaving this Gravemind in a mentally
: stunted status. This explains why the Flood on the Shield World have still
: been classified in the Feral stage.

I think it's more than that. By the time you encounter the Proto-Gravemind, the Flood has assimilated more sentient individuals than the one on the Infinite Succor did.
My theory is that the Flood is completely alien to life in the Milky Way. It doesn't think like us, it doesn't live like us, it doesn't experience the universe like us. Every time an infection form burrows into one of the Halo races, it has to get used not only to walking with two arms and two legs, but experiencing the universe through limited sight, sound, feel, taste, and smell. To their credit, they learn fast.

But what of a Proto-Gravemind that's not only stunted developmentally, but has developed perhaps tens of thousands of years without touching a single sentient being? It might be nearly impossible to communicate with. It might be set in ways too alien, too different to bridge the gap. It might not be able to adapt to us, not in an appreciable time frame.

One might even say that its way of thinking is...
*puts on a pair of Ray-Bans*
Calcified.

: If this is the case, then the preliminary classification system for Gravemind
: development that I started to work on above is most definitely wrong.
: Assuming that the above fact about the Halo Wars Proto-Gravemind is true,
: this means that Gravemind development should be broken into two categories
: for mental growth and for physical growth. Theoretically, you would need a
: certain amount of minds (and therefore, hosts) to allow a Gravemind to
: form. Determining approximately what that number might be would help,
: because then you could determine a minimum size. The only problem with
: that is that in the Halo universe, sentient life forms can come in all
: sizes, so I guess it would be an obsolete exercise.

The word you're looking for is "Futile", though that is probably too strong of a word.
Personally, I believe that there's probably a interplay between raw biomass and sentient thralls, but it can't be pinned down for one reason: The Flood doesn't play by rules. The Flood is mutable. The Flood is adaptive. The Flood finds a way, because unlike Life, it has a guiding intelligence behind it.