Early in the film Anna and Joy are seen in the Birch household watching a white rat. Later in the film, when Keller decides to take matters into his own hands and leaves to find Alex, the scene cuts again to the rat at Birch household, but now it is black, foreshadowing Keller Dover's transition from holy man to sinner.
The first time it was submitted to the MPAA, it received an NC-17 rating due to its tone and subject matter. The film's torture scenes were later cut by a couple of frames along with scenes suggesting pedophilia and it then received the R rating.
In this film a detective named Loki obsessively tries to find to kidnapped children. In Norse Mythology there is a tale (Loka Táttur) where the god Loki persistently tries to protect a child from a giant named Skrymir after Odin and Hönir tried and given up on the task.
Hugh Jackman portrays a father whose daughter is kidnapped and missing in this film. He was originally attached to play a similar role in The Lovely Bones (2009), but dropped out. That role was filled by Mark Wahlberg, who at one point was attached to play the lead role in this film.