What I could glean from the HB dream:
There was a previous experiment, which failed because the subject moved. They tried to fix it by keeping the subject in sleep paralysis.
(incidently, the previous subject is always MC-gendered).
The subject was super-cooled to a near death state. At least partially to suppress brain activity.
The test subject was remembering the scene from out of body. With their eyes closed. While in a REM state.
There were gates, which created some kind of ‘oscillation field’. The last gate created a ‘theta field’.
(theta fields are apparently associated with the hippocampal formation, which is associated with memory.)
Their purpose was apparently to ‘go deeper’ on a psychic level.
The subject ‘breached’ something. Momentarily. And brought something back with them, probably unwillingly.
‘It’ was lonely. And hungry. And it ‘ate’ the scientists, probably more in a mental instead of physical sense.
And then, when the MC came into contact with HB:
You relaxed too soon, you thought you had killed it, you let your guard down, and now it is inside and you can’t close the gate again, all nine of them are open, and it’s coming for you, and…
The whole thing was also strongly religious (nine walls, nine gates, a lot of praying) , though that might just be like the ‘I have become death’ thing from the nukes.