About 4 percent of pet owners have small animals, according to an online survey of 10,000 current pet owners by the American Pet Products Association, a not-for-profit industry group. And of those animal owners, only 6 percent own a rat or mouse — well behind guinea pigs (27 percent), rabbits (27 percent) and hamsters (25 percent), but ahead of gerbils (4 percent) and hermit crabs (2 percent).

Most pet rodents — such as gerbils, hamsters and guinea pigs — tend to bite, said veterinarian Cory Bassett, who specializes in exotic pet care in Overland Park, Kan. They are more antisocial and skittish because they are bred for quantity, not personality, she said.

But rats specifically bred to be pets, she said, are calm — and do not tend to bite the hand that feeds them, she said, and seem to bond emotionally with cage mates and owners.