Ever wonder what happens while you dream? Well, scientists theorize that by dreaming, you go to a different dimension in some way, and that ghosts/spirits are the deceased in a different dimension who are dreaming. If they injure/hurt, or even kill someone, that is what they are dreaming, and what we call poltergeists.
So I guess I really did no scope some people with a carrot shaped, colored, and ammo filled gun :T