Humans and dogs have been staring into each other's eyes for generations. Whether it's a pleading gaze for some leftovers, or a loving stare before a lick on the face, many dogs have mastered the art of making eye contact with their human companions.

You might think this is just a side effect of living with humans for thousands of years – an adaptation for easier communications – but there are multiple reasons for dogs to stare at humans, and a new study has found that some dogs are better at it than others.

"Mutual gaze also plays a role in dog–human bonding," the team writes in their new paper. "Its duration is associated with increased oxytocin levels in both dogs and their human partners."

The researchers measured a number of different factors to investigate what causes dogs to share more eye contact with humans. They measured the age and playfulness of the dogs around strangers, as well as the breed and traditional function that the dogs may have had.

They also took some measurements of the dogs' heads, known as their cephalic index.

41598 2021 88702 Fig1 HTML(Bognár et al., Scientific Reports, 2021)

You might not imagine that the ratio between a dog's snout length and head width would make much change to eye contact, but it actually produces a genuine difference in how these dog breeds see the world.

Short, thick-headed dogs can see less in their periphery than those with long thin heads, and past research has shown that those with shorter heads are more successful at following human gestures than those with long heads.

"It is likely that they see the human face more sharply because of their special retina, but it is also possible that their owners gaze at them more often as their facial features resemble a small child, a powerful cue for humans," said the first author of the study, ethologist Zsófia Bognár from Eötvös Loránd University in Hungary.

"Because of this, dogs with shorter noses may be more experienced in making eye contact… The boxer, bulldog, pug, and snub-nosed dogs, in general, have a more pronounced area centralis in the retina, so they can better respond to stimuli in the central field, which may make it easier for them to form eye contact with humans."

The team took 125 adult dogs through a series of experiments, including one where dogs were given a bit of sausage each time after making eye contact with the experimenter.

As you would expect, the team found the dogs got faster at making eye contact as the experiment went on, but they also discovered that numerous factors regarding the dogs' head sizes and breeds affected the speed and amount of eye contact between the different animals.

"Results showed that dogs with a higher cephalic index (shorter head) established eye contact faster," the team writes.

"Breed function also affected dogs' performance: cooperative breeds and mongrels established eye contact faster than dogs from non-cooperative breeds. Younger dogs formed eye contact faster than older ones. More playful dogs formed eye contact faster."

Who knew that the behavior of humans' best friends depended so much on the shape of their nose?

The research has been published in Scientific Reports.