Veterinarians and dog owners have always known that tail wagging is an important "body language" in dogs. In this study, 30 pet dogs were exposed to different stimuli (their owner, an unknown person, a cat, and an unfamiliar dominant dog). Dogs were placed in a box where they could only see what was placed in front of them. Each dog was exposed to all 4 stimuli 10 times during a 25-day period. Exposures were limited to 2 per day and were randomized to prevent habituation. Video frames were analyzed for tail wagging angle, strength, and direction. When dogs were exposed to their owners, unfamiliar people, or cats, they showed a strong bias toward right-sided wagging, but it varied in amplitude from high (owner), medium (unknown person), to low (cat). In contrast, when tested alone or in the presence of an unfamiliar dog there was a strong bias of tail wagging to the left. Stimuli associated with approach tendencies (eg, seeing the owner) were associated with right-sided movements or left brain activation. Stimuli associated with withdrawal tendencies (unknown dog) elicited left-sided movement or right-sided brain activation.

COMMENTARY: Canine tail wagging is a complex behavior that is not well understood. This article provides some new insights into the direction of tail wagging and its possible link to brain lateralization. Watching for left versus right tail wagging may be another postural cue for assessing the emotional state of our canine patients.

Asymmetric tail-wagging responses by dogs to different emotive stimuli. Quaranta A, Sinischalchi M, Vallortigara G. Current Biol 17:199-201, 2007.