I finally got my hands on Paranormal Activity 2 and watched it the night before last. Fear not, no spoilers, but for those on the fence, it is a prequel, not a sequel. That means it happens before the first movie. One last thing about the movie itself. I like the way that it works to lead into the events in the first movie. That's part of a topic for another day. The following has nothing to do with the movie in particular.
Last time the discussion involved in part two different types of haunting, one of which was unintelligent and repetitious. Apparitions that are an echo of the past or simply repeating events in their life after their death are generally limited to a single location. It is an interesting question to ask, what if they could be attached to an object, or in a real twist, a person. I'm sure there is likely real life lore somewhere about haunted objects with only a residual haunting rather than an intelligent force. As to the other...
One of the theories of repeat hauntings or echoes is that the nature and or structure of a location allows it to retain events and play them back when certain conditions are met. If a residual haunting was due to an anomalous energy source instead that energy might be attracted, like magnetism of a sort, to a living being of a compatible "polarity" such as any human. Such a person would then be haunted. This might not necessarily be enough for a haunting disturbance, whether poltergeist-like or with a looping apparition. It might be that only someone sensitive to the world beyond might witness the ghost or be plagued by moving objects. In a sense psychic energy from the human might be needed to fuel the haunting. It could make the difference between wispy half seen figures and ones indistinguishable from the living, or objects moved slowly in time versus hurtling through the air.
Whether the residual haunting "works" when no one is around is another matter regardless off its attachment to a place or object. The old question of "if a tree falls in a wood, does it make a sound" comes to mind. As far as physics go, the answer is yes that the tree makes a sound. These witness only hauntings may be different at your discretion, especially when speaking of visual apparitions. A ghost might not appear without someone to witness it. It might be something that happens entirely in the mind of the viewer, in which case the ghost will not appear in pictures or on video. Likewise with no human presence objects will not move around. This would separate poltergeist phenomena into being the product of an intelligent haunting or as the RSPK/psychic phenomena. Of course there is always leeway on these ideas and multiple mix and match options are open to the writer.
Music: The Game Never Ends by Stratovarius and by Let Me Hear You Scream by Ozzy Osbourne.