I don't think there are demons in the sense of this guy >
But I have heard so many accounts from ghosthunters, psychics, and on a personal level, from one of the church of England's senior exorcists.
There are spirit forms/energy forms that are not ghosts as we know them. We think of ghosts as being dead people, or the psychic residue of dead people. But according to the accounts that I refer to above, these energy forms are not human, nor have they ever been. One of the most common terms I've heard for them are elementals.
These things lurk around, basically, feeding on negative energy, or waiting to latch on to people. One warning I hear quite often about the ouija board, is that these entities pose as deceased relatives or friends in order to be
invited across.
Interestingly, despite my opening line, about them not having a traditional appearance, I have two personal accounts that contradict me.
In the last house I lived in (which could have an entire thread to itself), we suffered from an occasional loud knocking on doors in the upstairs rooms. My sister was doing a spot of spring cleaning one day, when she stopped dead in her tracks, and looked up at the door frame of my bedroom door. Just for a second she saw a small, leathery black creature perched there, then it was gone. Was this the thing that had been doing the knocking?
When I was a kid, and we were staying at my maternal grandparent's house, I was very ill with fever. I remember one afternoon being distressed because the room became full of swirling tiny bat like bird-things. My mother took me out of the room, sat me at the backdoor, and with a bit of fresh air, I was fine. For years I quite sensibly assumed it had been the fever making me see things. A couple of years ago, I was told about the time my grandfather had taken ill, some years after my experience, in the same room. Apparently, he had told someone he got a shock when he saw lots of bats in the room.