What could rats think when they laugh at us? That we, as humans, are ugly?

Various researches revealed that monkeys and dogs enjoy a good laugh. Now, it seems that rats do that too, pointing to the fact that people have been laughing for many millions of years, not ever since we turned into humans.

"Indeed, neural circuits for laughter exist in very ancient regions of the brain, and ancestral forms of play and laughter existed in other animals eons before we humans came along with our 'ha-ha-has' and verbal repartee," said Jaak Panksepp, a neuroscientist at Bowling Green State University.

The fact that human laughter starts very early is another clue that it's a deep-seated instinct.

"Young children, whose semantic sense of humor is marginal, laugh and shriek abundantly in the midst of their other rough-and-tumble activities. When chimps play and chase each other, they pant in a manner that is strikingly like human laughter," signals Panksepp.

Dogs, too, pant of joy. And rats' chirps during their playing resemble our giggles.

Panksepp has discovered that when rats are playfully tickled, they emit joyful chirps and bond socially with their human tickler, asking for more tickling and preferring the company of other chirpers.

Various researches confirm that laughter in animals is typically linked to similar play chasing and verbal jokes could tickle ancient circuits in the human brains. More research is required on this topic, explaining why humans like to joke around but also how the lack of laughter leads to depression.

"Although no one has investigated the possibility of rat humor, if it exists, it is likely to be heavily laced with slapstick. Even if adult rodents have no well-developed cognitive sense of humor, young rats have a marvelous sense of fun. Although some still regard laughter as a uniquely human trait, honed in the Pleistocene, the joke's on them." said Panksepp.