According to an on-set exorcist, one of his favorite scenes in the film because of its realism was when the weary psychiatrist expresses, "I didn't know I was in a fight," to which the demon responds, "That's why you're losing."
Sean Patrick Flanery explained in an interview that the script was so well-written that there was no improvisation from him, except for "Maybe two syllables."
Sean Patrick Flanery has explained that he took this role because it would help him remain true to himself and his faith.
According to "The Spirit World," a Catholic radio station program interview with a Vatican-approved priest/exorcist named Rev. Gary Thomas (whose experience as an apprentice to a veteran exorcist provided the basis for The Rite (2011), on which he was also a creative consultant), this was the most realistically accurate film about demonic possession the reverend had ever seen.