Trivia: Barney asks Drummer where Church is and Drummer replies "forget about him, he's out of the picture." A reference to Bruce Willis wanting too much money for his part in the film, hence he was cut out of the picture.
Trivia: The film was written to be a spin-off the "Paranormal Activity" series aimed primarily at a Latino market. Hence, it was not called "Paranormal Activity 5."
Trivia: The photos of Dreyfus' children are of Gary Oldman's children in real life.
Trivia: The original black Jaguar XJ6 Series III car, as used in the TV series of the same name, makes a cameo appearance in the background of the scene where McCall tortures the corrupt cop.
Trivia: Hollywood actress Reese Witherspoon was a fan of the novel and purchased the rights, intending to play the role of Amy herself. However, once David Fincher was attached as director, she opted to serve only as a producer, realizing she wasn't right for the role.
Trivia: Part of the inspiration for the film came from a friend of writer/director Jennifer Kent. Her friend, a single mother, had a young son who like many children was terrified of non-existent "monsters" he thought were lurking in his home. Kent then had the idea to turn this into a film. What if a child was terrified of monsters lurking in their closet, under their beds, etc... except they were real?
Trivia: Eva Green plays Shailene Woodley's mother in the film, even though in real life she's only 12 years older than Woodley.
Trivia: The fancy Mercedes is not "the only one in America" (as John Madec said on the movie) but the only one in the world. The car was borrowed for the purpose of the movie by one of the owners of the Formula One team McLaren and was shipped by air from Germany. Hence German licence plates often seen during the film.
Trivia: In Ben's taxi there's a rubber shark snout with teeth hanging from the rearview mirror. Ben is also the name of the fisherman in Jaws, whose decapitated head pops out underwater. Taxi driver Ben is even dressed similarly to the fisherman character in Jaws. In this movie taxi driver Ben is played by Judd Hirsch, who starred on the 70s-80s TV show Taxi, along with Christopher Lloyd and Danny DeVito.
Trivia: Josh Brolin Dwight had been previously portrayed by actor Clive Owen in the first film. As originally planned, Brolin would play the character prior to his plastic surgery, while Owen would reprise his role and play Dwight post plastic-surgery. However, Owen was unavailable to reprise his role, and thus prosthetics were used to attempt to make Brolin's post-surgery look subtly similar to Owen's facial structure.
