Many people have pets. Those of us who do have pets certainly love them very much. We become so close to our pets that we start to believe animals share human emotions. Well, your pet may not be able to feel all the emotions you can feel. However, animals and people share some of them. One of such traits is laughter. The theory that some animals like dogs, rats and apes can laugh was developed as long ago as 1872. Modern scientists have recently proved that most animals emit certain sounds in response to pleasure. You can hear such sounds when animals are playing with one another or with toys or when we tickle them. This sound is laughter. Of course, the sound of a laughing dog will be much different from the human laughter. It is nice to know our pets can laugh. Perhaps what they can laugh at is still a better mystery, though.