Any horror movie about "demons" is going to be completely inaccurate.
1.) There is no such thing as the typical hollywood "demonic possession". Demons have NO reason to possess people, and if they do it is CONSENSUAL BETWEEN ALL INVOLVED (and called invoking, not possession.)
2.) Related to the above... Exorcisms are completely fake (most of the time the "victim" is just having seizure problems, like the real-life counterpart of Emily Rose), or having some sort of mental trauma inflicted by xtian-type religions.
If it is "real", the enemy (usually a grey or reptilian, sometimes an enemy nordic) is usually just playing the possessor in an attempt to make it seem like the xtian-type religion has power.
3.) Last but not least, DEMONS DO NOT HAUNT/TORMENT PEOPLE.
As I have stated before, demons are HUMANITY'S GODS. If a demon has a problem with somebody, that person is no more. Demons also have a damn good reason for offing somebody (like that time Bastet killed a cat mass murderer, or the time Lilith murdered a politician for stomping on women's rights.)
Please try to remember this, and put a stop to this nonsense... even if that means simply walking out on a movie and doing something else for a few hours. Do not support the enemy's slander and filth buy purchasing such items as well.