Guinea pigs are rodents commonly kept as pets in a similar manner to rabbits. They are ideal for small children as they have a placid temperament and are large enough to be handled without causing distress to the animal (unlike some smaller pets such as hamsters). Like most rodents, guinea pigs can give birth to large litters of young and thus care should be taken when selecting males and females as pets. As with rabbits, they eat vegetables such as carrots and lettuce and are easy to feed and take care of.
Guinea pigs are used for the purposes of testing drugs and cosmetics before trials on humans, as are rats, mice and other small rodents. Because of this, the term to be guinea pigs is sometimes used to describe someone or a group of people who are testing or trialling something for the first time, for example a class of students may say "we we're guinea pigs for the new course structure".