Emotional support animals come in all shapes and sizes—as large and ostentatious as a miniature horse or full-sized peacock, or as unobtrusive as a well-trained guinea pig. Some offer support via timely yaps, others by quiet companionship. Some are friends to all, others take their work too seriously to bother with strangers. In the US, most public places are under no obligation to make any allowance for these animals, whatever their demeanor or size. The Americans with Disabilities Act (ADA) defines service animals in terms of their extensive training—think guide dogs or medical-emergency animals that receive months of specialized instruction....