Pure and utter nonsense. There's no spirits, or ghosts, or monsters, or haunted houses, etc. This stuff is for superstitious or ignorant people.
When people think they're possessed, they ACT like they're possessed, and, to an ignorant person, it can seem as if they are "possessed." We've all seen where preachers do their speeches, and yelling, and shaking, etc. etc. and the whole congregation gets into a fervor. Then the preacher comes down and places his hand on some lady's head and then she falls back and starts shaking while the preacher is doing his psychobabble and "Thank you, Jesus!!" bit, and then the lady acts like she's possessed. I have no doubt that that lady actually believes that the preacher is calling out her demons, but it's nothing more than mass hypnosis and hysteria.
Well, you did ask.