"Dogs can pick up emotional cues from another dog by watching the direction of its wagging tail, a study suggests.These results suggest that dogs have perceptual and attentional asymmetries so for example, if you are going to visit a dog, if you are vet, there will be probably a side which is better with respect to the probability to evoke a more friendship response or to evoke a more aggressive response,"," says Vallortigara https://www.npr.org/2013/11/01/242126859/the-tails-the-tell-dog-wags-can-mean-friend-or-foe