Stage actors have used the phrase "(stage) business" for a long, long time to mean the incidental activities performed by an actor for dramatic effect--the lighting of a cigarette, the mixing of a drink, the crushing of a flower. (Ask around among theatrical actors and see what "a bit of business" means to them.) I've tried to find when the phrase entered English in a theatrical context with no luck so far, but I'd be shocked if this didn't come to the world of film from theatre. Perhaps a reader with an academic background in English-language theatre could comment?

I read this Lubitsch quote and thought of you, Scott: "It is the task of the scenarist to invent little pieces of business that are so characteristic and give so deep an insight into his creatures, that their personalities clearly and organically unfold before the eyes of the audience so that the latter feel that the actions of these people are contingent upon their characters, that there exists some kind of a logical fate, and that nothing is left to mere accident or coincidence...." -- Ernst Lubitsch (I don't have a date for the the quote, though; sorry.)