A saying in English says a dog is man's best friend. Dogs and humans have shared close relationships for thousands of years. Scientists believe the bond between humans and dogs is deeper than we thought. They found that dogs cry with joy when they see their owner after a period of absence. The scientists did a small study on 22 dogs. They tested the behaviour of the dogs. They looked at how the dogs reacted when they were reunited with their owners, and with other people they saw every day. The scientists said that when the dogs saw their owners, they cried.

The researchers put strips of paper under the dogs' eyes. They used the paper to check if the dogs cried. The scientists found that when dogs saw their owners after five to seven hours of separation, they shed tears. A researcher said he had never heard of animals crying tears of joy, when reuniting with their owners. He said: "Tears might play a role in the deepening of mutual relationships." He thinks dogs' 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."