Proverbs 17:3 (NLT version) states, "Fire tests the purity of silver and gold, but the LORD tests the heart."
Sam and Dean use the same Fish and Wildlife IDs that they used in Dead in the Water (2005)--Agent Mark Hamill and Agent Dean Ford, respectively. This is a nod to Star Wars actors Mark Hamill & Harrison Ford.
This is the 11th episode directed by Richard Speight Jr.. He also played the archangel Gabriel in 12 episodes.
This is the first episode where the title is taken directly from the Bible.