My little dutch bun is a tail wagger. It is usually a very fast little tail shake in her case. She is the first rabbit I have ever known who did this, and it is so cute. She does it quite a lot, but so far I have not really found any reasoning for it. She never really seems annoyed to me, so I just think of her as a jolly little bun, kind of like a golden retriever who express happiness through tail wagging. I would be interested to hear what others think.