- Rochelle Aytes - Savannah Hayes
- Finn Carr - Young Spencer Reid
- V.J. Foster - Daniel Adams
- Pete Freeland - Lawyer
- Victor J. Ho - Barry Plyman
- Aubrey Plaza - Cat Adams
- Erich Riegelmann - Barry Winslow
- Mark Semos - Zac Rubenis
- Kai Stein - Little Boy
- Aisha Tyler - Doctor Tara Lewis
- An uncredited actress - Sharon Mayford
- "I Put A Spell On You" by Hit Crew Masters
- Spencer Reid: "Just as the constant increase of entropy is the basic law of the universe, so it is the basic law of life to struggle against entropy." — Vaclav Havel
- In physics, entropy is a thermodynamic quantity that represents the unavailability of a system's thermal energy for conversion into mechanical work. The term is often interpreted as the measure for disorder or randomness in the system, and has also been used as a word for "lack of order or predictability; gradual decline into disorder".
- Harry & Glenn's Grill and Bar, the primary setting of the episode, was named after show producers Harry Bring and Glenn Kershaw.
- ↑ http://www.cbs.com/shows/criminal_minds/photos/1005587/insider-facts-from-criminal-minds-entropy-/101062/what-s-in-a-name-/