Normally we would think that ghost is from the "soul" of a living thing. If that is the case, then the world would be full of ghosts - and certainly this does not look so. I would think that someone becomes a ghost when he/she/it has something undone when he/she/it dies. So, he/she/it is trying to have the outstanding thing done before moving to the right world he/she/it should go to.

sarah..