The Rat gets the last laugh

EXN.ca | Discovery: "Ever notice the laughter of children? They laugh freely and easily without having to understand a joke. They're generally more ticklish than adults and often, the mere suggestion that they may get tickled starts them laughing. Just saying Koochi-koochi-coo without the accompanying tickle makes children break out in a fit of giggles.

Well, two American scientists say it's the same for mammals, including the most basic – the rat.

They've tickled rats and found that they make the same chirping sounds as they do when they're playing with each other. The younger rats 'laughed' more than the older rats when tickled just as among humans."

And just how do you tickle a rat?