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According to a new study by Japanese researchers, dogs cry when they reunite with their owners. Additionally, it seems that the blubbing is related to oxytocin levels, known as the “bonding hormone.”

The discovery, which was published last week in Current Biology Magazine, calls into question the long-held belief that humans are the only species capable of producing tears as an emotional response.

Based on the behavior of 22 dogs, the study examined the emotions of dogs who were reunited with their owners and other people they knew.

To put their theory to the test, researchers from Azabu University and Jichi Medical University taped strips of paper to the dogs’ eyes. The Schirmer tear test was used by the researchers to measure the dogs’ tear volume before and after the reunions. The test is commonly used to determine whether an animal or human produces enough tears to keep their eyes wet.

Filter paper is put inside the lower eyelid in small pieces. The tears are absorbed by the paper, and the volume is then determined.

The tear volume was measured in the dog’s home setting with their owners present and again shortly after the dog and owner were reunited after being separated for five to seven hours for the experiment.

The researchers also compared the quantity of tears shed when the dogs were reunited with people they knew but who were not their owners.

To determine if the tears were related to their emotions, the researchers gave the dogs a solution containing oxytocin, a key hormone involved in bonding. They discovered that after using the hormone, the dogs’ tears increased considerably. While dogs have been known to cry in order to keep their tear ducts clean, it has never been related to their emotional response.

“We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners,” said Takefumi Kikusui, one of the authors of the study in the journal Current Biology.

“Their tears might play a role in the deepening of mutual relationships and further leading to interspecies bonding,” the researchers wrote.