... In contrast to an emotional-support animal (E.S.A.), a service dog is trained to perform specific tasks, such as pulling a wheelchair and responding to seizures. The I.R.S. classifies these dogs as a deductible medical expense, whereas an emotional-support animal is more like a blankie. An E.S.A. is defined by the government as an untrained companion of any species that provides solace to someone with a disability, such as anxiety or depression. The rights of anyone who has such an animal are laid out in two laws. The Fair Housing Act says that you and your E.S.A. can live in housing that prohibits pets. The Air Carrier Access Act entitles you to fly with your E.S.A. at no extra charge, although airlines typically require the animal to stay on your lap or under the seat—this rules out emotional-support rhinoceroses. Both acts stipulate that you must have a corroborating letter from a health professional....