7. The Haunting
Often it's hinted in "Paranormal Activity" that much of what occurs in the house could be due to Katie's own psyche and her shady past as a child involving illness and family secrets. Perhaps she's not totally possessed by the demon as she is being mentally broken from an already frail mental state, and is allowing the demon access. Much of what occurs in the original film is reminiscent of the Robert Wise directed "The Haunting" in which Claire Bloom plays a woman being terrified by ghosts in a very gorgeous mansion. Though the group in the house are battered and taunted by unseen demonic forces, most of what occurs is hinted at being mostly in the main characters Eleanore's mind due to her mental illness. It's a film well worth watching.