People say dogs are man's best friends. Dogs and humans have always been close. Scientists think the bond is very deep. They said dogs cry with joy when they see their owner after being away for a long time. The scientists said when dogs see their owner, they cry. When they see other people they know, they don't cry.

The researchers said when dogs see their owners after five hours of being apart, they cry. A researcher said he had never heard of animals crying tears of joy. He thinks dogs' tears make humans love their dogs more. He said: "It's possible that dogs who show tears…during human interaction would be cared for more."