Tired dog lovers who think their pet pooch is yawning right along with them may just be right, according to a Japanese study.
Dubbed "contagious yawning", the new research says man's best friend can sense human fatigue and, in a possible show of empathy, will join humans in a big yawn.
Canines yawn more often when it's their owner who's involved, added the study conducted by researchers at Tokyo and Kyoto universities, which was published in US science journal PLOS One this week.
"Our study suggests that contagious yawning in dogs is emotionally connected in a way similar to humans," said Teresa Romero of the University of Tokyo who led the study.
Romero's team measured the dogs' heart rate while observing their response to human yawning. She said this allowed researchers to rule out the possibility that the dog yawns were just a stress response.
The study observed two dozen canines to see how they reacted both to their owners and to unfamiliar humans. The people involved in the experiment also made other facial expressions to see if the dogs sensed the difference.
"The occurrence of yawn contagion was significantly higher during the yawning condition than during the control mouth movements," the study said, adding that "the dogs yawned more frequently when watching the familiar model than the unfamiliar one".
Similar behavior has been seen in primates including chimpanzees, it said, adding that contagious yawning in humans is associated with activity in the part of the brain responsible for feelings of empathy.