By examining dogs’ interactions with people and other animals, scientists have found that a dog wags its tail to the right when it spots someone or something familiar such as their owner and to the left when it feels threatened.
The bias is subtle, requiring video analysis to spot, and not obvious enough for you to tell whether the next dog you meet is going to lick your face or turn tail. The study of wagging could be used in animal welfare to help vets to gauge an animal’s state of mind.
Shown a human, tails wagged consistently to the right. They carefully studied the tail wagging angle and ignored twitches of less than three degrees overall, “which were plausibly not correlated to wagging”.
They found that the unfamiliar person elicited less wagging than the owner, and the cat the least wagging of all, though still slightly to the right – probably because the dog was so keen to give chase that it was distracted.
Shown a large, unfamiliar and intimidating dog, the dogs wagged their tails more to the left.
Dogs also wagged to the left when on their own without anyone to look at, suggesting that they like company.
In dogs, as in humans, the left side of the brain is involved in signaling to approach something while the right side advises retreat.
Dogs are already known to prefer to use one paw over the other – most male dogs are left-pawed, whereas females show a lesser tendency to right-pawedness.