There is a saying in English that says a dog is a man's (and woman's) best friend. Dogs and humans have shared close and loving relationships for thousands of years. Scientists believe the bond between humans and dogs is deeper than we thought. The scientists discovered that dogs cry tears of joy when they see their owners after a period of absence. The scientists conducted a small-scale study on 22 dogs. They tested the behaviour of the dogs. In particular, they looked at how the dogs reacted when they were reunited with their owners and with other people they had daily contact with. The scientists said that when the dogs saw their owners, they cried.

The researchers, from Azabu University and Jichi Medical University, put strips of paper under the dogs' eyes. They then checked to see if, and when, the dogs cried. The scientists found that when the humans and dogs were reunited after five to seven hours of separation, the dogs shed tears. Researcher Takefumi Kikusui said: "We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners." He added: "Their tears might play a role in the deepening of mutual relationships." He believes the tears may make humans love their dogs more. He said: "It's possible that dogs who show teary eyes during human interaction would be cared for more."