Q. I have often read the ending credits and wondered exactly what each person’s job is. At the end of “The Perfect Storm,” I saw credits for “assistant director,” “second assistant director” and “second second assistant director.” Now I just have to ask: Exactly what does a “second second assistant director” do? Alan Altman, New Fairfield, Conn.

A. I referred your query to the writer-director Kevin Smith (”Clerks,” “Chasing Amy,” “Dogma”), who replies:

“The term `second second AD’ is really a smoke screen. This term is employed in movies as a polite way of saying `third AD.’ If you say `third AD’ really fast, many times, you might notice how easy it would be to say `turd AD.’ According to lore on the set, that’s why ADs opted for `second second’ as opposed to simply `third’–because people on set never missed an opportunity to refer to them as `the turd.’

“The actual job of the third AD, or second second, is to carry out the second AD’s wishes. The job of the second AD is to carry out the assistant director’s wishes. The job of the assistant director is to make the director’s life miserable by constantly reminding him or her that we’re running behind schedule. In essence, the entire AD team is on set solely to enrage the director (well, that and to direct background action of extras, bring the actors to and from their trailers and have the talent sign out after the shooting day is completed). An interesting sidenote–it’s the job of the AD to utter those immortal words `Stand by for picture,’ and `Roll sound,’ and in the case of some extremely lazy directors, `Action.’ ”