Dogs make puppy dog eyes for the benefit of humans and rarely use the imploring facial expression when on their own, a new study has shown.

It has long been assumed that animal facial expressions are involuntary and dependent on emotional state rather than a way to communicate.

But scientists at the University’s Dog Cognition Centre at Portsmouth University have found that dogs mostly use facial expressions when humans are present, as a direct response to attention.

Puppy dog eyes, in which the brow is raised to make the eyes appear wider and sadder, was found to be the most commonly used expression in the study. Researchers do not know whether the dogs are aware they look sadder, or have just learned that widening their eyes elicits sympathy and affection in humans.