Imagine being laid up in a hospital and, as you're wheeled down the sterile hallway, along strolls a three-foot-tall horse wearing yellow rubber booties and a backpack full of daisies. No, you're not having a morphine——induced hallucination, you haven't died and landed in some kind of surreal Barnum &Bailey heaven. You've just met Lucky Boy, one of the thousands of animals making the rounds at hospitals across the United States. Fifteen years ago it used to be unusual to see a dog or cat in a hospital, but now even miniature horses like Lucky Boy are lumbering down the corridors. And as animal-assisted therapy continues to grow in popularity, a range of pets worthy of Noah's Ark is turning up in medical centers——everything from pot-bellied pigs, pigmy goats and parrots, to pet chickens, giant rats and llamas. The greater presence of animals in health-care settings comes amid increasing evidence that pets are good for us and can play a significant role in patients' recovery. Sometimes known as 'pet therapy,' animal-assisted therapy and activities have become an important tool for doctors and rehabilitation specialists. 'Animals motivate people to participate in their therapies, brighten patients' days, give them a chance to talk about the animals in their lives, and give them the opportunity to forget that they're in a hospital,' says Dianne Bell, coordinator of the Delta Society Pet Partners program, which helps train and register animals and their owners for volunteer positions in health- care settings. Currently there are more than 8,000 Delta Society Pet Partner teams in the United States and a handful of other countries, says Bell. Each makes an average of three visits per month and is likely to touch the lives of more than 540 people per year. And these figures don't include the hundreds of other volunteer teams registered through different programs. According to the passage, pets are used in health-care settings mainly because _________.