popular pets are noted for their loyal or playful characteristics, for
their attractive appearance, or for their song. Pets also generally seem
to provide their owners with non-trivial health benefits; keeping pets has
been shown to help relieve stress. There is now a medically-approved class
of "therapy animals," mostly dogs, who are brought to visit confined
humans. Walking a dog can provide both the owner and the dog with
exercise, fresh air, and social interaction.