When the characters speak Italian they all do so with heavy American accents. The list includes: (1) Guard at the Centrino Assylum (2) Possessed girl on the Vatican tape (3) Police officers who go into Ben's and Michael's apartment
When the film begins with the 911 recording the date is stated to have been October 30, 1989. However, when the police chief is talking on the news later he states that dispatch received a call late the night of October 20th.
When Maria is thrown off the table during her exorcism, one of cameras shows her heart monitor with her vitals flashing. They should not be reading anything as the throw would have disconnected the wires.
The interior of the plane traveling to Rome is that of a TAROM Romanian Air Transport aircraft. Logos of the airline are visible on headrest covers and the overhead exit sign is in Romanian. The movie was shot in Romania.