It was also a Ra'ta'ha— the demonic water-weasel that liked to play in rivers and streams and tie weeds around people's feet to see if they would drown. It also looked remarkably like an otter, so no one would suspect otherwise. That was probably for the best. An otter was acceptable, and he worried that maybe she would summon a Patronus of something that looked a bit too much like he did in his true form— utterly demonic and alien.