Though it may sound like one, this is no joke: Two miniature horses trotted into a hospital. Doctors and patients did double-takes when the equine visitors ambled down long corridors in the pediatric unit at Chicago's Rush University Medical Center. Wide-eyed youngsters hooked up to IV poles stepped into hallways to get a glimpse, and kids too sick to leave their rooms beamed with delight when the little long-lashed horses showed up for some bedside nuzzling. Mystery and Lunar, small as big dogs, are equines on a medical mission to offer comfort care and distraction therapy for ailing patients. It is a role often taken on by dogs in health care settings — animal therapy, according to studies and anecdotal reports, may benefit health, perhaps even speeding healing and recovery.