During an August 2014 interview with New York Magazine, Tyler Perry said that he didn't know anything about the movie's source novel or its director, David Fincher, and that he wouldn't have accepted his role in the movie if he had: "I probably would have walked away from it. If I had known who David Fincher was, and his body of work, or if I'd known the book was so popular, I would have said, 'No.' And my agent knew that! He didn't tell me until after I signed on!"
David Fincher's musical brief to Trent Reznor and Atticus Ross was based upon a visit he paid to a spa wherein the music meant to relax him he perceived as creepy and made him feel uncomfortable. This gave him the idea to set the music as though it is passive and relaxing but actually instills a sense of dread.
When Nick explains to the police that he hasn't called Amy's parents because there's no signal in the building, his left hand is empty. In the next shot, his cellphone is in his left hand.
The toll free tip number set up by Amy's parents is shown onscreen many times and even stated in dialogue as "1-855-4-AMY-TIPS." Yet when Amy goes to the www.findamazingamy.com website about halfway through the movie, the phone number listed in huge print is not the same, there it is "1-800-FIND-AMY".