As if we needed more evidence that dogs are man's best friend.

Previous research delving into canine psychology has shown that when dogs and humans look at each other, they experience a rise in oxytocin – the "love hormone" that makes you feel warm and fuzzy around friends, family, and significant others.

This new study published by the University of Helsinki, however, is the first to discover that dogs love seeing humans smile so much, they were willing to override their fear-based instincts for the sake of adoration.

The team at the school's Canine Mind project conducted two different tests on 43 hounds. For each test, the dogs would be shown two different images: a picture of an angry human face followed by a smiling human face.

Since a dog's pupils will dilate at whatever it feels is the most powerful emotion or detail, the researchers used an eye-measuring device to monitor the dog's emotional reactions to each image.

For the first test, dogs experienced the most visceral reactions to the images of angry humans because they felt threatened. This is to be expected considering a dog's survival instincts are programmed to react to danger and aggression.

For the second test, however, the dogs viewed the images while under the influence of oxytocin – and the researchers were surprised to find that the pups' pupils dilated in response to the smiles, rather than the frowns. This means that they ignored their survival instincts in favor of a set of pearly whites.

"We were among the first researchers in the world to use pupil measurements in the evaluation of dogs' emotional states. This method had previously only been used on humans and apes," says Professor Outi Vainio, who headed the research group.

"Both effects promote dog-human communication and the development of affectionate relations," says Professor Vainio.

Now, the only thing left to do is figure out whether cats are looking at us lovingly because we're carrying a food bowl or because our fingers provide the most optimal head scratches.

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