I’ve always assumed that humans were the only animals to laugh and that the cute noises that dolphins and chimps and friends make are just coincidentally similar to human laughter.
I might be wrong, if this finding, described at Animal Wise holds up.
As they progressed with their research, Panksepp and his colleagues found that many of their rats seemed irresistibly drawn to tickling, chasing after the ticklers and making substantially more play chirps while being tickled than during any other behavior. But the researchers werenâ€™t content with anecdotal observations, and over the course of several years and a number of experiments, they systematically documented a dozen separate lines of evidence suggesting that the ratsâ€™ tickle chirping corresponded behaviorally to playful laughter in young human children.
The Rat Tickler
Animal Wise has plenty more great articles like this one. I recommend it for home-schooled (and regularly-schooled) kids.