Do you ever find clues, a sort of forensic trail in a novel which leads you to suspect what the author might have been reading when (s)he wrote it?
Obviously, I have an example.
I've just started reading Case Histories, by Kate Atkinson, and the book I read before that was Christie Malry's Own Double-Entry by BS Johnson - two books with little if any apparent similarity except that they are both good. Anyway, early on in the Atkinson book, we meet a character whose brother-in-law was a polar explorer, and I thought, hmm. Haven't I just read a book where the main character's father was a polar explorer? Oh yes, it was Christie Malry. Anyway, not a particularly interesting coincidence, so I didn't dwell on it and moved on. Then, only a few pages later in the Atkinson, I came across this: "Sometimes it seemed to him as if the entire world consisted of one accounting sheet - lost on one side, found on the other." Which really made me stop, because that's the basis of the entire plot of Christie Malry's Own Double-Entry (the double-entry in question refering to accountancy, and not to something you might have to search for on more dubiously-oriented websites.)
I don't think it's plagiarism and I don't think there's anything wrong with it. I just find it interesting (assuming that was the book she was reading, and not just two coincidences in a row) how little bits of the writer's real world can end up in their fiction.