Wilford's line that "the shadows on my cave wall haven't said much about you" is a reference to The Allegory Of The Cave from Plato's Republic in which people chained up in a cave with their backs to the entrance try to determine the nature of the world outside based only on the shadows cast on the wall before them. This mirrors Wilford's efforts this season to determine Snowpiercer's route and purpose based on very limited data while in prison.
Miss Audrey says to Till "it's perfectly acceptable to build a fortress around yourself." Actress Mickey Sumner's father is singer/songwriter Sting, who had hit in the '80's with the song "Fortress Around Your Heart".