https://www.youtube.com/watch?v=hSFg_HI_xSQ
It looks like the headcrab is eating the head of it’s host.
That’s true, most parasites do not kill their hosts. Parasitoids, on the other hand, do, and they intend to from the beginning. Many species on earth do this. In fact, about 10% of all described insect species are classified as parasitoids.
However, I do agree with you about the zombies talking, at least that it requires a brain. I touched on this before, but if the headcrab bypasses most of the brain and goes for the spinal cord instead, it can directly control the movement of the host without taking over higher functions such as speech, allowing the zombified host to cry out in pain and for help. If the headcrab did control the entire brain, I find it highly unlikely that it would use human words. Even if it did use human words, why would it ask for help?
What puzzles me is why the zombines can still create speech without a brain, because the evidence I see points to the headcrabs controlling them without them having heads. The device implanted in the trans-humans’ throats could have something to do with it. However, it is an alien and a trans-human interacting. It could be that something about their coupling causes the upper part of the head to come off when the host body dies.
In any case, it’s all fictional stuff, so until Valve says anything definite, no theory is provable. To me it looks like the missing heads of the zombine are a mystery Valve intended to plant for a while and then reveal the answer later.
My theory is that headcrabs simply use the technology at the inside of the body of the zombines (which is put there by the combine) to walk around and stuff in a similair or maybe even the same way they do with normal hosts. This might indicate that they use something that’s hidden inside their body to control the body, rather than use some chemical or something. I mean along the lines of extra limbs, designed to enter the body and control it. I also have a theory of were the limbs enter the body. This theory would also explain some things about normal zombies. Well, here it goes: You know how the heads of a zombie are almost always turned with their face towards the gap on the bottom of the headcrab, right? Well, my theory is the limbs enter the body via the eyes. This would also explain why zombies yell “my eyes sting!” when their screams are played backwards. But yeah, that’s my theory.
My theory is that it’s just a game. It’s not meant to be completely believable.
it is a mystery
We’re still allowed to speculate about it, so STFU.
Headcrab connects to brain of its host. It probably sends ton of possible signals (there is probably stage, when whole “zombie” shakes, makes random moves and screams etc.), and figures how does the host works (and in which direction host moves, so that it can place itself directly in this position), then mutates it. Combine Soldiers had their brains mostly replaced by tech, which is useless for headcrab, so they somehow remove it till they reach only part of brain that is left - consciousness, and after that they can use the host. How they use the combine speech generator? This thing is plugged into the consciousness part of brain, so that it converts his thoughts into speech, and if there is tension and need for fast reactions, it converts it into one of the fast reached prerecorded communicates. Also, these prerecorded communicates may have some automatic system that turns them on, and fight with headcrab is definitely one of moments when this thing would work. Headcrab uses hosts voice only to distract and scare its enemies, so it does not not matters what does it says or screams - it feels that it is loud, headcrab is satisfied with the effect.
My theory is that the modifications made to the combine actually make the heads of combine more sensitive to the decay brought about by zombification, so when the headcrab pulls itself off of a human host, the hosts head still has enough tensile strength to remain attached, but when the headcrab pulls away from a combien host, the tensile strength fails resulting in the head staying with the headcrab to be digested.
Maybe they ate away at their brain, and then just controlled the nervous system which was mostly replaced by technology probably, considering they don’t feel any pain (the soldiers I mean). This wouldn’t be very hard for such an adaptable creature, considering they mutated into three kinds of headcrabs, possibly even more, and managed to adapt tp radiation so they can survive in pools of toxic waste.
Why same type headcrab would eat brain of host type 1, and leave the second type host almost untouched? If there would be a reason for headcrab to do it, all of them would do it.
Brains are used by headcrabs, not eaten. Headcrab cracks everything on its way to the brain, tech included.
I heard that the host is merely unconscious. Alive but unable to control the body. Hence the screaming noises. The headcrab needs the host to be alive.
I’ve always believed that the headcrab removes the Zombine’s head because the circutry and computer stuff makes it unusable, so they must connect directly to the spinal cord.
By the way, guys, the zombine’s radio chatter is probably from other, non-headcrabbed soldiers.
my theory: The Zombine is not talking the radio is. as for the HL2 beta zombie idk
So did I 
Well, you can have have this:
Now you can have back your thread 
/OCD
+1 for teh jokerine
The way I see it, the headcrab has three major organs used for interaction with the host’s head. The first are the teeth that are plainly visible on all headcrabs sav Lamaar, these are used to fasten the headcrab tightly on the host skull. The second is the infamous beak, which, like most beaks in nature, will be used for cracking things open, in this case the skull. The third organ would be a series of tendrils that lower into the host brain and release chemical signals to force the host to engage in such and such an action, no matter what the conscious host would rather do.
For Zombine, the brain, now filled with microchips and circuitry, will not properly respond to the chemical signals, and so therefore the headcrab either breaks down the majority, or can only latch on combine whose heads are already wheedled down to the brain stem due to prior trauma. As such, complex actions such as speech and tactics (e.g. grenades) are still present and broadcasting as the remnants of the circuitry.
very nice, but claws & elongated fingers is kinda redundant.
- Dress Shoes
- Blue Jeans
- Sweater
Well, fingernails and fingers themselves are different things I’d say, but I guess you got a point. I 'll try to fix it later today. I wish I could’ve done something like this though… I would do it if I had the skills! I may fire up model viewer today and take some pics for it 
Because there’s a helmet on the second one. And maybe because the headcrab “knows” something we don’t. Afterall: The headcrab probably has more experience at latching ontop of a head than we do.