 In the scene where Roy Fuchs (Jack Warden) walks up to Rudy (Kurt  Russell) and Jeff (Gerrit Graham) as theyre finishing shoveling  dirt over the spot where they buried Luke, Gerrit Graham didnt have  any lines and kept pestering Robert Zemeckis and Bob Gale for lines.  Finally, he just decides to repeat whatever Kurt Russell said to  Jack Warden. Appearently, Warden was unaware of what Graham was  doing, thus his line "Whatre you? A fuckin parrot?". It was  Wardens genuine annoyance at Graham which worked so well in the  scene that it was included in the film.