Do animals laugh too?

It may seem like a strange question, but I am serious. I think I have seen my dog laughing or what appears to be laughing on more than one occassion. I'm wondering if anyone else has ever seen what appears to be an animal laughing. I do know for sure that dogs can smile, laughing may be possible for man's best friend as well. Oh, and please don't move this thread to the folk lore section, thanks.

Many primates laugh, but this is in no way an expression of happiness. They tend to do this to express their panic or fear. This is said to be carried to humans on a different level. If you tickle kids, they laugh, but that doesn't mean they are enjoying it. They tend to squirm for a reason.

On a side note, Hyenas make a noise similar to that of a human's laugh.