Question: are we the only animal that laughs?

Bridget Waller answered on 14 Jun 2010:

Many primates (e.g. chimpanzees, gorillas, orangutans) make a similar sound to human laughter when they are playing, and they make a similar facial expression (mouth open, jaw dropped, lip corners curled upwards). We think this is the same as human laughter, and has evolved to have a similar function. In fact, there are probably many animals that make similar sounds that could be similar to laughter – rats make a high pitched noise when they are tickled!