While many people believe that laughter is exclusively a human trait,

While many people believe that laughter is exclusively a human trait, research suggests that this ability is actually shared by several nonhuman animals. It has been observed frequently in chimpanzees, even as early as 1827, when Darwin wrote about them making laughter-like sounds while play-fighting.

These sounds are very different from typical human laughter, which can make them difficult to identify. Chimpanzee laughter is produced while both inhaling and exhaling, which makes it sound more like breathing or panting. Interestingly, this is very similar to the way human infants laugh. However, older human children and adults laugh only when exhaling, which results in vowel-like sounds that chimpanzee laughter lacks.

Rats have also been observed producing laughing sounds. In some experiments, the laughter is elicited by tickling the rats, a method that has also been used to make chimpanzees laugh. As with chimpanzee laughter, rat laughter can be difficult to identify, but mostly because of its unusually high pitch.

Dolphins have also been observed making laughing sounds. Researchers found that dolphins will make certain sounds only when play-fighting. When dolphins engage in aggressive fighting, they will not produce the laughing sounds. This suggests that laughter can help animals differentiate between play-fighting and actual aggression.

1. According to the passage, each of the following is true of chimpanzees EXCEPT

A. their laughing sounds are similar to those made by human infants
B. they laugh while inhaling and exhaling
C. they laugh when they engage in play-fighting
D. they sometimes produce vowel sounds while laughing
E. they can produce laughter when tickled


2. The primary purpose of the passage is to

A. argue for further research into a certain behavior
B. show the similarities and differences between one animal’s behavior and another’s
C. provide evidence against a common belief about a certain behavior
D. dispute the claims of scientists about animal behavior
E. explain why humans and other animals are different