Dogs use facial expressions to show they are happy to see their owners, a new study has found. Japanese researchers have decoded body language in dogs and found that the canines tended to move their left eyebrow upwards around half a second after seeing their owner.
The study tracked changes in the faces of dogs in the moments they were reunited with their owners or when meeting a stranger for the first time.
When the animals were introduced to someone they had never met before, they moved their left ear back slightly, a newspaper reported.
If they were presented with an object they didn't like, such as pair nail clippers, the animals moved their right ear instead.
"It is difficult to explain this difference in movement between the ears and eyebrows. Dogs' ears are prominent features used to convey emotional expression, therefore our results suggest that dogs were more cautious toward unfamiliar people," said Dr Miho Nagasawa, from the department of animal science at Azabu University in Sagamihara, Japan.
"In contrast, eyebrow movement might indicate a visible response where by dogs attempted to look at their owners more intently," Nagasawa said.
In the study, 12 dogs were placed in a room divided by a partition with some black curtains that opened briefly to all the dogs to glimpse what was on the other side.
Coloured tags were placed on the dog's faces to allow a high speed camera to track the movement of their features.
When the curtain opened, their owner, a stranger, a toy or an item they did not like was on the other side, allowing the researchers to record their response.
They found that the dogs moved their eyebrows upwards whenever they saw someone behind the screen, but far more when it was their owner, particularly on the left side.
The researchers suggested the subtle changes on different sides of their face are a reflection of activity in key parts of the brain that control emotions.
They also believe it could because the animals were experiencing conflicted emotions - joy at seeing their owner but sadness at not being able to reach them through the partition.
"Ownership is a significant social factor for dogs. This suggests that human-dog bonding relationships have a biological basis," Nagasawa said.
"Canids are highly social and communicate using an abundant array of facial expressions. These communication methods might play an important role in their communication with humans," Nagasawa added.
The study is published in the journal Behavioural Processes.