This brings up to my memory one episode which never was explained. There was a period when I shared a house with a house mate and his doberman Razor. One night when I was alone at home with Razor, being a huge lapdog he was he was resting on top of me in a lazyboy chair while I watched the telly. Then he suddenly sprung up, stared at the other settee and started growling fiercely. He was a big baby and in spite of being a doberman he was not at all a sort to act aggressive for no particular reason, and as I said there was no one else at home and obviously no one or nothing on the settee. He kept on for about half a minute, then stopped, curled up and went back to sleep. His sight was perfectly normal for a dog, and no one could ever figure out what was the matter.
This happened only once, but as I hear animals can sense spirits and stuff much more keenly than humans and such, it really spooks me to this day!!