It's Gettin' Dark, Too Dark To See

"This was for a particular scene in the movie when Slim Pickens is dying and that’s the first time I ever cried while I played. It was the combination of the words, Bob [Dylan]’s voice, the actual music itself, the changes, and seeing the screen…In those days you were on a big soundstage, and you had this massive screen that you can see on the wall, [with] the scene…running when you’re playing. I cried through that whole take.” - Jim Keltner, drummer on Bob Dylan's original recording of "Knockin' On Heaven's Door" (as quoted in Bob Dylan: The Complete Guide)

(Sadly, embedding is disabled for the clip Keltner describes in the above quote. I've included a YouTube video below featuring only the audio of the song, but I'd encourage you to also watch the film clip.)