Rats 'like a laugh'

It is not known if rat jokes exist

Scientists say giggling, ticklish rats have provided them with the first credible evidence that animals unrelated to humans can laugh.

For years biologists have known that chimpanzees and even some monkeys produce a panting noise akin to human laughter.

But there is scant evidence that other animals are capable of laughter.

Now two American scientists are claiming to have discovered that rats "laugh" when tickled.

Inaudible to humans

Rat laughter is not the same as humans, however. It consists of high-pitched, chirping whistles, outside the range of human hearing.

The noises have been detected before but were previously believed to signal distress, aggression, or sexual excitement.

Jaak Panksepp and Jeffrey Burgdorf, of Bowling Green State University in Ohio, found that young rats chirp vigorously during rough-and-tumble play sessions.

They also chirped more than their older relatives when tickled. According to the scientists, this fits in with the idea that children are more ticklish than adults.

Tickling experiments

Mr Panksepp and Mr Burgdorf believe the tickling experiments show that a "primal form of laughter" evolved well before primates appeared.

They suggest that both rats and primates use laughter to distinguish playful from threatening physical behaviour.

Mr Panksepp told New Scientist magazine: "We'd be surprised if rats have a sense of humour, but they clearly have a sense of fun."

A laughter expert from the University of Maryland, Baltimore, Robert Provine, believed many social mammals probably produced laughter-like sounds.

But he told New Scientist it took an "intuitive leap" to recognise the calls as laughter, because the sounds were very different.