Laughter when defined is to make sounds from the throat while breathing out in short bursts or gasps as way of expressing amusement.  

Because of close association with humans, domesticated dogs are known to exhibit laughter too.     

For centuries man has converted the wild dog into a yipping, yapping and laughing pet dog. To the human ear a dogs laugh sounds similar to a normal pant. With the use of a spectrograph, the pants vary with bursts and frequencies, which is likened to a laugh.

 To get your dog to laugh you just have to execute a play-signal. Your pet, being very sensitive to your movements and feelings, would take up on your signal and utter barks, growls, whines and a breathy exhalation. A playful time may tire your dog but the brightness of eyes and the goofy smile shows you it was worth it.  

In a dog shelter, where canines are isolated from one another and tender human contact makes a high-stress environment where dogs are unruly and exhibit aggression be able to prove that the spectrograph recording is indeed a laugh, scientists played a recording of the produced “dog-laughter”. As the recording ended, dog wagging and mimicry of the dog laughter replaced aggression. The study showed that a pro-active reaction of the shelter dogs to the recording.  

A laugh, which is contagious, gives off positive energy. I guess what the study didn’t point out was that; the wild side (canine or human) diminishes with a good belly laugh.