Being fluffy and soft makes this friendly rodent, the Guinea pig, one of the more popular household pets. In the scientific community, however, Guinea pigs are used as animal models and are the subject of experiments. Thanks to its physiological similarities to us, in its hearing, immune system and respiratory tract, the Guinea pig makes a valuable model of study in medical and physiological research. Guinea pigs were not always treated as test subjects. They were (and still are) a popular South American food staple.