If you watch enough Animal Planet or even your own animals, you discover that there are a couple of things that seem to transcend species: The joy of playing with a ball (I was amazed to see even turtles bumping a ball around), and getting their head scratched. We humans tend to anthropomorphize animals a bit too much, and view a dog baring its teeth as "smiling" (while it's a warning), and think cats are plotting evil when their eyes are half-closed (while in fact, that is friendliness). We humans consider a direct gaze or bared teeth friendly, something our pets eventually get used to, even though in their world, an indirect gaze or closed mouth is friendlier.
But there may be other human reactions we truly share with animals - like laughter. Researchers have found that rats enjoy being tickled - and even produce a laugh-like sound. It's inaudible to human ears, but slowed down to a frequency we can hear, it does sound giggly.
By the way, I love the way the rats look in this video: Well-fed, healthy and energetic. Lovely animals!
This tidbit brought to you by someone born in the year of the Rat. And yes, I laugh when tickled. I'm very ticklish.