New research published in the journal "Current Biology" says your dog may shed a few tears of joy when he or she sees you after a long time. This is the first time research linked dog tears with emotion. Takefumi Kikusui, a professor at the Laboratory of Human-Animal Interaction and Reciprocity at Ababa University in Japan, decided to investigate tears in dogs after a poodle became misty-eyed while nursing her puppies. That gave Kikusui the idea that oxytocin, the maternal or love hormone, causes eyes to tear in dogs. Researchers found the volume of tears increase when dogs are reunited with their owners as opposed to a stranger. Adding oxytocin to their eyes further increases the volume. Asked to rate pictures of dogs' faces with and without tears, participants gave a more positive response to teary-eyed dogs. Though more research is needed -- scientists don't know if negative emotions produce dog tears, too -- the team is confident the research reflects the impact of the dog-human bond.