The name of Milton's friend, Webster, could be derived from the short story "The Devil and Daniel Webster." In the story, Webster is hired to defend someone against the devil.
When Milton watches Frank hit Piper from the phone booth, a small sign is visible that reads "Mona Elkins Realty". It has a picture of the same Mona with whom Frank was cheating on Piper, but with clothes on.
When Milton and Piper are driving down the road, they run over a dead snake. This is a foreshadowing to symbolize good overcoming evil (snake=serpent=devil).
Near the end of the motor-home chase, the trunk lid of the Charger is damaged and flapping open as the car goes over bumps, but when they stop beside the road, the trunk lid is closed and shows no visible damage.
After the shoot-out is over when Milton is having sex with the waitress from the bar, he is between her legs which are wide open. In the very next cut as he stands up, the legs of the waitress are tightly closed together.