The next time you see a dog wagging its tail, look a little more closely. You may be able to detect that the tail sweeps slightly more toward one side of the dog’s body. This asymmetry isn’t random. When dogs see something they want to approach (like their owners) they wag to their right. When they see something that makes them wary, like a strange dog, they wag to their left.
Most of the time, you’re not going to notice the difference. Humans don’t usually place that much importance on the nuances of tail wagging. However, dogs might have a different perspective. Scientists led by Marcello Siniscalchi of the University of Bari Aldo Moro found that dogs do indeed pay attention to other dogs’ wagging habits.
The scientists showed dogs video clips of other dogs, wagging either to the left or to the right.
The test dogs’s heart rates were elevated when they watched another dog wagging to the left. They also exhibited more anxious behavior when seeing a left-wagging dog compared to a right-wagging dog. In fact, dogs were more relaxed when viewing a dog wagging its tail to the right than when watching a motionless dog.
While the observing dogs may have been picking up other cues besides just the tail wags, these data do suggest that dogs pay attention to other dogs' tails, and that they can communicate their emotion state via the direction of their tail wags.Siniscalchi M, Lusito R, Vallortigara G, & Quaranta A (2013). Seeing Left- or Right-Asymmetric Tail Wagging Produces Different Emotional Responses in Dogs. Current biology : CB PMID: 24184108