Do you believe other animals laugh too?

You only have to look at the primates closest to humans to see that laughter is clearly not unique to us. I don't find this too surprising, because we're only one among many social species and there's no reason why we should have a monopoly on laughter as a social tool. The great apes, such as chimpanzees, do something similar to humans. They open their mouths wide, expose their teeth, retract the corners of their lips, and make loud and repetitive vocalisations in situations that tend to evoke human laughter, like when playing with one another or with humans, or when tickled. Laughter may even have evolved long before primates. We know that dogs at play have strange patterns of exhalation that differ from other sounds made during passive or aggressive confrontation.

But I think we need to be careful about over-interpreting panting behaviour in animals at play. It's nice to think of it as homologous to human laughter, but it could just be something similar but with entirely different purposes and evolutionary advantages.

Everything humans do has a function, and laughing is no exception. Its function is surely communication. We need to build social structures in order to live well in our society and evolution has selected laughter as a useful device for promoting social communication. In other words, it must have a survival advantage for the species.