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"Don't look now, but is your dog laughing?"

That was the headline in Science News as it described what could be one of the most unique animal experiments ever.

For the first time, researchers have discovered what could be evidence a dog has its own form of laughter.

Don't believe it? Science Specialist Ed Yeates reports.

When Patricia Simonet from Sierra Nevada College presented her findings before the National Animal Behavior Society Conference, they couldn't believe their ears!

In an animal's own subtle way, the dogs in Simonet's experiment were "howling with laughter."

Hey dogs, did you ever hear the one about the Labrador who walked into the bar?

If you expect to see dogs laughing like we define laughter, it won't happen like this. And if they really do chuckle in their own way, it won't be to our human jokes.

But if you play with a dog, you might hear something other than the panting or playful growls -- a sound which Patricia Simonet claims is distinctively a laughing dog.

She began documenting the sound while dogs were at play. The distinctive, breathy exhalation was only present when they were having a good time.

Patricia Simonet / Sierra Nevada College: "IT BECAME VERY CLEAR THAT THIS WAS SOMETHING MORE THAN A DOG PANTING WHEN WE SAW THE GRAPHS OF THE TWO VOCALIZATIONS."

ED YEATES, SCIENCE SPECIALIST: "DR. SIMONET AND HER COLLEAGUES AT FIRST TRIED RECORDING THE SOUNDS IN A PUBLIC PARK WHERE GROUPS OF DOGS WERE PLAYING TOGETHER. SHE SOON REALIZED SHE HAD TO HAVE A CONTROLLED EXPERIMENT."

So, as summer ended, the team moved indoors. With background noise eliminated, cameras and parabolic microphones followed a variety of dogs at play.

Simonet says if it's true dogs have been domesticated and sharing their time with humans for about the past 100-thousand years....

SIMONET: "THAT IT WOULD MAKE SENSE THAT THEY WOULD HAVE IN AN EVOLUTIONARY OR BIOLOGICAL SENSE SIMILAR VOCALIZATIONS, TO MEAN SIMILAR KINDS OF THINGS."

The sound is so distinctive from others that a new dog in the room immediately moves to the source of the recording, looking for the playmate who is allegedly laughing.

Earlier in her research, Simonet observed a puppy - spinning a chair around with its paws.

SIMONET: "AND AS IT SPUN, HE WOULD START DOING THIS HAAAAAA - AND JUST ROLLING HIS HEAD BACK AND COMING BACK LIKE HE WAS HAVING A BELLY LAUGH."

The team is now ready to move into the next phase of its studies, searching for would-be communication nuances and subtleties which are in frequencies higher than the human ear can detect.

"WE DON'T KNOW WHAT WE'LL GET. AND WE'RE ALSO GOING OVER SOME DATA TOO ON PLAY AND ROLE REVERSALS AND RULES THAT DOGS MAKE UP DURING PLAY."

From the Divine Songs for Children, "Let dogs delight to just bark and bite, for God hath made them so." Or did He do more?

Animal researchers are intrigued with Simonet's studies but say more testing is needed before they propose that non-human primates, dogs or even rodents laugh.

Incidentally, government researchers have recorded a chirping sound rats make when they're playing with other rats or if you tickle their bellies.