They love to go places in pockets or just hang out on your shoulder or lap. Most are smart enough to cage train themselves almost immediately. This story will come as no surprise to those who have, or have had, rats as pets. Psychologists in the U.S. claim to have the first credible evidence that animals other than humans and our close cousins are capable of laughter. For years, biologists have known that chimpanzees and even some monkeys produce a panting sound similar to human laughter, but evidence of mirth among other mammals has been sketchy at best.
Rats respond to tickling by emitting whistles outside our range of hearing.
These chirpings have been detected before, but most researchers thought they signaled distress or aggression, or were a prelude to sex. But the Ohio researchers found that young rats chirp vigorously during play sessions with each other. They also chirp more than their elders when they are tickled, which Panksepp says fits with the idea that children are more ticklish than adults. He suggests that rats and primates, especially the young, use laughter to distinguish playful from threatening physical interactions, New Scientist says. Panksepp expects many scientists to be skeptical about claims for human emotions in a lower species, but he points out that our laughter is triggered by brain regions that evolved from ancient times.