That the tailbone seems to act on its own as if it had a mind of its own, I think is related to your focus and that of other ghosts or people around. Changing focus using your vestibular or the whistling in your ears while with ghosts is important to passing along a tail wag. While wobbling my knee mimicking my tail wag I noticed that the wobble will change in pace and pause on its own in accordance with a stress in my ear from presumable the attention of ghosts in the room. By wobbling the knee intentionally in a clockwise then counter clockwise gesture I can make the tails of the ghosts stop wagging. I've also become aware of patterns of how the tail wagging of a ghost is predictable and what there next move will be, still unexplained at this point because it happens fast. Right now I'm practicing using slight movements as well as focus and breathing to stimulate and stop the tail intentionally. Those are also predictable, like I can tell after a thought effects me emotionally what gesture i will make with my head or legs or other to stop myself and ghosts from making me dizzy with the tail.