Once again, the player piano is playing another modern instrumental version of the tune, "No Surprises" by the U.K. Band Radiohead.
Because of a presidential debate occurring on the day of the release, HBO decided that regardless of the regular airing of the episode, they'll release it 3 days earlier by surprise, on their streaming services.
Clifton Collins Jr.'s gun belt is the same one his real-life grandfather Pedro Gonzalez Gonzalez wore as part of his Rio Bravo (1959) costume.
Towards the beginning when William is getting dressed into character he has a choice of a white or black cowboy hat. This is a recurring theme representing good -vs- evil. I.E. "The Man In Black". The same theme was used throughout the ABC series "Lost".