" The source can even be us. Humans store energy. It’s a fact. And because no sighting of a spirit can happen without a human observer present, it’s assumed that ghosts borrow the energy of the living to build strength and make their presence known through sight or sound. It’s why people sometimes feel suddenly lethargic or the hairs on their arms and neck stand up. It’s a physical response to their personal energy being gathered by ghosts and almost always precedes a paranormal encounter. "

― Zak Bagans , Dark World: Into the Shadows with the Lead Investigator of The Ghost Adventures Crew