While previous research had revealed that dogs wag their tails more to the right (from the canine’s point of view) when they are happy and to the left when they are nervous, the authors of the new study report that other dogs can detect and respond to those differences, said BBC World Service Science Reporter Rebecca Morelle.

“To find out more about how dogs react to the lop-sided tail wags of other dogs, the researchers monitored the animals as they watched films of other dogs,” Morelle said. “When the animals saw an otherwise expressionless dog move its tail to the right (from the tail-wagging dog’s point of view), they stayed perfectly relaxed.”