A Ghost is the soul of a deceased individual that fails to pass over to a spirit realm and wanders around the living world for various reasons. Ghosts haunt mostly the location of the ghost's death, and sometimes locations where they're conjured by either family members, friends, or anyone. 

Ghosts have different personalities if they died peacefully and wanting to comfort their mourning loved ones, they would find ways to communicate to make them to comfort them out of mourning, but if a ghost died tragically, in one case, at the hands of another person, the ghost tends to have hostile, vengeful personality that includes haunting people in a hostile way. Sometimes a ghost can move out of its recently deceased body and confused. Other times, a ghost can refuse to pass over due to fears of being held accountable for the deeds they've done on Earth.  

Animals have a stronger ability than humans to sense the supernatural, when dogs sense a ghost, or in one case, see a ghost while its human master cannot, they behave strangely by starring at walls, starring at something in the space they possess, but when there is a hostile spirit, they bark uncontrollably and behave in a hostile manner, sometimes not necessarily against their masters.  

Attempts to conjure a ghost, or communicate with one can lead to negative consequences, including unintentionally opening a portal between the physical world and the spirit realm where it might include Demons.