While captive Travis (Cliff Curtis) is asked if he is Mexican or Persian before he states he is Maori. This could be a nod to the fact that Curtis has played a number of roles in the past where he played Latino (such as Training Day or Columbina) or middle eastern (such as Three Kings (1999) or The Insider (1999)) characters.
200 rats were sent crawling over Noel Fisher in the scene where he opens up a wall that's making weird noises. The rats were kept on set for nearly a week so they would be nice and relaxed for their big moment.
When Travis throws the cement block at the soldier Willy, it was an unscripted moment. Cliff Curtis did it on the spur of the moment.
Daniel Sharman and Sam Underwood join the cast. Ironically, while the two are playing brothers from a rural part of California, both of them are actually English.