I love this

Just yesterday someone on the street said to me:

"Your dog looks like he’s smiling at me!"

So I was delighted by this article on the BBC site

Animal laughs no joke says expert
Many animals may have their own forms of laughter, says a US researcher writing in the magazine Science.

"Such knowledge may help to reveal how joking and horsing around emerged"
                                          –-Jaak Panksepp, Bowling Green State University