When dogs like someone, their tails wag more to the right, when they don’t, their wagging is mostly to the left, found neuroscientist Giorgio Vallortigara (University of Triste, Italy) and others in a recent study called "Asymmetric tail-wagging responses by dogs to different emotive stimuli." Most animals, including birds, fish and frogs, show some variation of emotional asymmetry in the brain. For humans, the left brain is linked to positive feelings, attachment and love, safety and calm, as well as a slow heart rate. While, the right brain is associated with negative feelings, fear and hate, depression, rapid heart rate and the shutdown of the digestive system. In broader terms, the left controls behaviors of approach and energy enrichment, the right, withdrawal and energy expenditure. It’s important to note that asymmetries appear on opposite sides of the body, as the left brain controls the right side, the right - the left. So, in reading people’s faces, it is the movements on the right side that reflect happiness, the left - unhappiness. For the tail-wagging experiment, Vallortigara took 30 mixed breed dogs and put them in camera-monitored cages, where they were shown either their owner, an unfamiliar human, a cat, or an unfamiliar, dominant dog. Each instance lasted 90 second, 10 sessions a day for 25 days. As to be expected, the pets’ tails wagged the furthest to the right when they saw their owners, moderately with a human stranger, a little bit with cats, and strongly to the left with aggressive dogs.

This adds to the growing body of evidence that brain asymmetry, once attributed only to humans, is present in most animals. Bees learn better with their right antenna. Chameleons are more likely to change color out of fear when they see someone from their left eye. Chickens look down with their left eye to look for food while keeping the right watching for predators overhead. Chimpanzees, when excited negatively, tend to scratch themselves on the left side. Furthermore, left-handed chimps are more frightened in general by new stimuli than the right-handed, their right brain making them more wary. All this is rather curious, seeing how many languages have some sort of synonimity between right (dexter) and good on the one hand, left (sinister) and bad on the other. It seems on some level, the distinction between the brain hemispheres and their domains has long since been recognized. Sometimes, this manifested in interesting ways, e.g. in the Middle Ages, left-handed people could not become knights, even though, as anyone who has fenced can testify, they would have made exceptional fighters, since not only are most people unaccustomed to fighting the left-handed minority, but the spiral stairs in castle towers are designed to put right-handed attackers at a disadvantage. Also, it would be interesting to look, from a holistic perspective, how physical changes on different sides of the body effect personality and behavior. Because, it seems to me that I’ve been getting more moody and paranoid as vision in my right eye worsened. Could it be the same as with the chameleons? And are pirates portrayed one-eyed for the same reason (it sure isn’t for depth perception)? That would be a whole other study.

If you want to know if Spot loves you so, it’s in his tail, NYTimes.com