Maybe these terms are wrong but, I will try to explain my thoughts. I remember a movie and you guys will probably also remember, The Skeleton Key. Of course that movie still... a movie (duh), but where I live, we have many 'paths' originated from africa, and the master or priest (I don't know exactly the name) is responsible to receive MANY spirits (another name here) in his body to exchange for some works. If you think the spirits are astral beings, COULD someone be inside another body (not with both astral body, of course) in any way ?
It would probably be very difficult and require a ton of practice, meaning you'd almost certainly need the permission of the person you're taking possession of, but I think it's possible. Not really practical, though, you could communicate far more efficiently through other methods and I can't imagine using this technique for anything important or stressful. Unless a person is in a deep trance (even then there are serious limitations) they can easily snap out of this on reflex, an ill-advised thing to do while your body is in motion.