This is Scientific Americans, 60-Second Science. I'm Karen Hopkins.

After an exhausting day at the office, it's hard not to smile when you're greeted by

a delirious display of uncontrolled canine joy. But it's not just that happy yapping and

wriggling tailwagging that tug at our heartstrings. Because a new study shows that dog's eyes fill

with tears when reunited with their people and affect that evokes our nurturing instincts.

The findings appear in the journal Current Biology. Takahumi Kikusui became interested

in doggy's damp and adoring gazes while watching his pet poodle interact with her

pubs. At some point, Kikusui, who is a professor of veterinary medicine at Asabu University

in Japan, realized that his adorable mama dog had tears in her eyes. That potential connection

between unbearable cuteness and unshed tears sent Kikusui scurrying away from his poodle

and back to the lab. In the test, we initially measured baseline tear volumes when dogs

were together with the owner in their house. Then, the owner would high-tail it off for

five or six hours. When the owner came back, we measured tear volume again and found that

the reunion with the owner stimulates the tear secretion. But it only worked with the dog's

owner. There was no increase with tear when the dogs were separated from the owner and

we united with the dog's caretaker in a dog care center.

The researchers suspected that the tearful reaction was stimulated by oxytocin, a hormone

associated with social bonding. They'd shown previously that oxytocin is boosted when

dogs interact with their owners. And oxytocin receptors have been found to be abundant

in the glands that secrete tears in mice. So we applied oxytocin to the dog's eyes.

And voila, the dogs grew weepy. But to what end? In other words, is there some benefit to this

lacrimos behavior? To find out, Kikusui and his colleagues showed volunteers a couple of

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