Tail bob could be natural, or some people do dock mixes.
Story about that: When I worked for a vet, a client found a newborn puppy abandoned in a dumpster. Brought it in. We treated her, she survived. We found her a home. She was black & tan, and people became convinced she was a Rottie mix, partly because one of the vet techs insisted that the black on her toes meant she was. (argggh.) So they decided to dock the tail. I'm all "NO, she looks nothing like a Rott, bad idea!"
Grown up, she proved that a husky mix looks pretty goofy without a tail.
(sorry for the OT, I just find it funny.)