well as metioned before : ghosts or "shadow things" can be what ever you want ....but in most cases they are mainly due to your own mind . You see even how you remember certain events can make a simple skampering squril seem like "some sinister evil force" ... also if you are a bit freaked out allready it's pretty easy to be intimidated by the unknown : remember that time when you were all alone in your house and you heard some weird noises ?