You know I'm in on this one lol.
Animal have greater senses then people. It's a known fact. In saying that, they are super sensitive of the paranormal. Often times they sense things way before we do.
For example: While I was a keeper aid at my local zoo, I was cleaning stalls of the sloth bears. The male was familiar with my presence, my smell ect. I had some strange things happen that were paranormal while in that particular part of the zoo. For some strange reason, Franci would charge in my direction for no reason. Before or after the charging, I would feel someone tap on my head or arm when no one else was with me. I believe it was a spirit and the bear sensed it.
Even if it is a non threatening spirit, animals react defensively when they sense something off around them...unknown energy.