From wikipedia:
"As of September of 2010, the United States' Americans with Disabilities Act has redefined a service animal as "any dog that is individually trained to do work or perform tasks for the benefit of an individual with a disability, including a physical, sensory, psychiatric, intellectual, or other mental disability. Other species of animals, whether wild or domestic, trained or untrained, are not service animals for the purposes of this definition."[4] This revised definition excludes all comfort animals, which are pets that owners keep with them for emotional reasons. (For example, the owner may feel calmer when he or she is near the pet.) Unlike a service animal, a comfort animal is not trained to perform specific, measurable tasks directly related to the person's disability. Common tasks for service animals include flipping light switches, picking up dropped objects, alerting the person to an alarm, or similar disability-related tasks.
There is no license or registration process for service animals in the United States. As a result, any person could claim that any animal was a "service animal" and demand to bring it into places where animals are normally banned, such as food preparation areas, hospitals, pet-free apartment complexes, and airplanes. A primary goal in revising the definition was to reduce abuse and fraud committed by people who falsely claimed that their cats, birds, ferrets, reptiles and other pets were service animals."
