Sandra Blakeslee | Trieste | April 24

NYT - Every dog lover knows how a pooch expresses its feelings.

Ears close to the head, tense posture, and tail straight out from the body means “don’t mess with me.” Ears perked up, wriggly body and vigorously wagging tail means “I am sooo happy to see you!”

But there is another, newly discovered, feature of dog body language that may surprise attentive pet owners and experts in canine behavior. When dogs feel fundamentally positive about something or someone, their tails wag more to the right side of their rumps. When they have negative feelings, their tail wagging is biased to the left.

A study describing the phenomenon, “Asymmetric tail-wagging responses by dogs to different emotive stimuli,” appeared in the March 20 issue of Current Biology. The authors are Giorgio Vallortigara, a neuroscientist at the University of Trieste in Italy, and two veterinarians, Angelo Quaranta and Marcello Siniscalchi, at the University of Bari, also in Italy.

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While some researchers have argued that only humans show brain asymmetry — based on the evolution of language in the left brain — strong left and right biases are showing up in the brains of many so-called simpler creatures, said Lesley Rogers, a neuroscientist who studies brain asymmetry at the University of New England in Armidale, Australia.