Dogs laugh, but they do not emit the same sound as humans when they laugh. A dog at play sometimes appears to smile, with his mouth open and his tongue hanging out, making a sound like panting. This noise has been linked with dog laughter in a number of studies.
To the untrained ear, the sound of a dog's laughter may sound no different than the typical pant of exhaustion. However, the noise frequency is more broad than that of panting and has been shown to have a calming effect on other dogs when played via recording. Humans may even be able to imitate the sound to calm their own dogs.