Kib can't so much flee. He can shriek - he can lurch in the direction of the nearest house and try the door - it's locked. He can amble briskly...
He can break into a run when the snake gains on him and fall flat on his face.
And he can get eaten up.
And it's too bright too bright too bright and he flings his arm over his eyes.
He gets a lot of Harthanic-intensive dreams and when he's up he writes Fëanáro summarizing the phenomenon asking if there's an obvious interesting way to study the progression of his language fluency without confounding it.
Then it'd be easy to test his vocabulary and reading but hard to test them in a way that wouldn't make him better at the language, and they can't even use anyone else doing the same vocabulary and reading exercises as a control because people vary so much in language-learning ability and the only other human here is three weeks old.
Yeah, that was about as far as he got on the question too. Since there's nothing worth preserving about Kib's half-ignorance of the language... Well, since Fëanáro presumably only knows how to read Harthanic and the things that Kib is pretty sure he can reproduce flawlessly are the accent and fluid casual grammar maybe they should go have Harthanic conversations?
So Kib goes down to his place and demonstrates an extremely limited vocabulary with nearly native ability to reassign the parts of speech of words, produce natural-sounding compounds, and deploy Harthanic's several varieties of syntactically meaningful reduplication.
"It's weird," Kib comments, "I think I'm getting most of my vocabulary from actual dream-induced memory, which is why it's so spotty and I can talk about dolphins and not chickens and stuff like that, but I think I'm getting most of the grammar and so on from remembering being somebody who had access to it rather than from remembering actually using or thinking about it. Might be some kind of procedural/factual distinction."
"She was a servantmaker too so that's hopelessly confounded, I didn't notice a jump in how good I was at assembling chassis or programming or anything when the dreams got underway. And I've always spent a lot of time just reading. She cooked more than I've tended to, I guess?"
"Yeah, inconveniently being the same person means we spent a lot of our time in the same ways."
"New Kib would have a different name. ...Possibly a suspiciously similar one though, Alymbel, Akibel..."
"Yeah, but it's separately inexplicable, I don't see how the creche workers could have been influenced that way."