There's this tiny, completely inconsequential line I think about constantly. We're introduced to an incredibly stern astropath (the choir master, I think) and, as we're getting his description, we get this line: "...and - not that anyone would guess it - he had a fantastic singing voice."
He dies almost immediately, and I fixate on what a weirdly deep insight that is for a throwaway line and character. He exists for maybe 5 seconds of story time, but now I know forever that he had an expressive hobby that he chose not to show anybody. It just feels like it says so much for something that doesn't really matter.
Do you have any weird little lines or moments that stick in your mind like that? Also, does anyone know what book I'm talking about? I think it's early on in the Heresy, but I'm not completely sure.