It has long been held that only humans may shed happy or sad tears. No other animal is known to shed tears of emotion.
However, a controversial set of tests using man's closest friend have been conducted by Japanese experts who have adopted that supposition.
They contend that the eyes of our canine companions are also filled with emotion.
According to the study, when dogs are reunited with their owners after being apart for a day, they don't just whimper with joy; they also appear to be excitedly crying.
When the dogs greeted their owners, the researchers observed a 10% increase in tear volume (relative to average wetness) in 18 canines.
The dogs, however, remained calm when they encountered a well-known non-owner.