Was originally rated R by the MPAA for "violence, terror and disturbing images" but the film was eventually edited to receive a PG-13 rating for "mature thematic material involving violence and disturbing sequences."
While promoting the film on Craig Ferguson [airdate 8/29/12], Jeffrey Dean Morgan reported that strange incidents took place during production that couldn't be explained. Lights exploded during the filming of key scenes; and just two days after wrapping principal photography, all of the props for the film, stored in case of re-shoots, were destroyed in a fire that mysteriously erupted from within the storage-house.
The trivia items below may give away important plot points.
In the final scenes Em takes hiding in the hospital's morgue. A hospital's morgue plays a crucial part in Ole Bornedal's breakthrough movie Nightwatch (1997).