One of the reasons dogs make such great companions is that they’re so good at communicating with us. They wear their emotions on their faces far more than most non-human animals. We've now discovered that’s because they are aware we’re watching, and have learned that humans are visual creatures who respond to facial cues.

At the University of Portsmouth's Dog Cognition Center (a marvelous thing in itself), Dr Juliane Kaminski filmed dogs in different contexts see how much the presence of humans influenced their facial expressions.

"The findings appear to support evidence dogs are sensitive to humans' attention and that expressions are potentially active attempts to communicate, not simple emotional displays," Kaminski said in a statement.

If facial movements were something dogs did when they were excited, for example, Kaminski expected to see them when given food treats. However, in Scientific Reports Kaminski reveals the 24 dogs in her study showed no difference in facial response when given food, as long as no one was watching.

On the other hand, the raising of the eyebrows, which makes their eyes look larger and more adorable, was more common when the dogs knew they had human attention. Dogs that could see a person watching also showed their tongues and vocalized more. They were no more likely to sit or stand, however.

Kaminski conducted her study using a range of ages and breeds to make sure what she found is representative of dogs in general. She filmed the dogs tied on a lead with a person standing a meter away, but sometimes looking at the dog, and at other times distracted so they faced away. The dogs’ responses were tracked using DogFACS, a coding system that records movements of canine facial muscles, including those so subtle we would not normally be conscious of them.

Thousands of years of domestication have changed both dogs and humans. As a result, they are far more attuned to us than other animals. Previous studies have shown dogs are more likely to steal food when a human’s back is turned, and can follow a human’s gaze only if eye-contact is made first.

In this context, it’s not all that surprising that dogs adjust their expressions to elicit a human response. Nevertheless, even some human facial expressions are involuntary, and there has been a general assumption, including by Darwin, that animals’ facial expressions are based on their internal state, rather than their audience.

Domestication is not essential, however, if an animal is sufficiently smart. Some apes have been shown to alter their facial expressions depending on whether they know anyone is watching.