Everything Else . Tail motion, plus eye contact, are key parts of a complicated inborn system of communication among dogs. The signals let dogs figure out who is top dog in a group or when meeting a stranger. They can also communicate emotional states. In some cases, tail wagging may simply indicate excitement.
Position is important, too.
The tail held high is a signal of dominance, which may be challenged or not, and a tucked tail shows a dog is kowtowing or accepts lower status. When wolves challenge each other, they try to monitor the signs of the autonomic nervous system, like heart rate and blood pressure, that indicate emotion. Some of these signs are read indirectly, through changes in the pupil of the eye. If the pupil becomes wider, it generally means fear or at least ambivalence. If a wolf's pupils narrow, on the other hand, taking into account other postures and signs, it generally means the wolf is angry, and should be taken seriously.