They locked them out of language when they tried to ask for help. Not because anybody would have helped but because it was easier than pretending not to understand. They talk to themselves in memories and fears not knowing which is which.
They weren't asked. That memory is clear. They remember thinking I didn't say yes to this as the needle broke the skin and something was added to the blood and taken from themselves.
There's the memory of an explanation about what it was. Is. A machine that was an organism and also a computer but mostly a self-expanding biological factory: it turned out you didn't have to cure cancer to make money off it. (It hadn't been one of the scientists explaining but a nurse hitting on them. When they asked why they needed to use it in humans she had made an unreadable gesture and left.)
(Humans have brains. It's not the only difference. Perhaps their nightmares are just nightmares and they are alone in their too-tight skull.)(That's a fear expressed as its opposite.)
There's a memory of pain.
There's fear of pain.
The moment when the thing inside kills the thing it's inside of (or the other way around) without malice intent or care cannot be a memory it has to be a fear but it feels like a memory.
They know this death isn't a memory because they remember asking the technician about to put a barrier between consciousness and words what they were going to farm from the thing growing inside them, if the thing itself or something it secreted, not because they cared but because they were desperate to talk while they still could. They remember the technician saying that if it had survived it would have been valuable on itself.
The last thing they could have asked but were too shocked to was but then why? Then they lost language behind an infinite wall of burned synapses. But they didn't need words to feel in their flesh bones that it was because it was easier to hurt them as planned than to change their minds not to.
(One died first, then the other. There was regret for the technical loss, quiet to protect the stock price, and NDAs would have silenced the parents of the host.)