Legal definitions

Hamilton is a "Service Animal" with the specialization of "Hearing (Ear) Dog"

Dog: four-legged animal, canine. If you need more than this to define 'dog', please use Google.

Service Animal:
"Service animal means any dog or other common domestic animal individually trained to do work or perform tasks for the benefit of an individual with a disability, including, but not limited to, guiding individuals who are blind or have low vision, alerting individuals who are deaf or hard of hearing to the presence of people or sounds, providing minimal protection or rescue work, pulling a wheelchair, fetching items, assisting an individual during a seizure, retrieving medicine or the telephone, providing physical support and assistance with balance and stability to individuals with mobility disabilities, and assisting individuals, including those with cognitive disabilities, with navigation.

The term service animal includes individually trained animals that do work or perform tasks for the benefit of individuals with disabilities, including psychiatric, cognitive, and mental disabilities.

The term service animal does not include wild animals (including nonhuman primates born in captivity), reptiles, rabbits, farm animals (including any breed of horse, miniature horse, pony, pig, or goat), ferrets, amphibians, and rodents.

Animals whose sole function is to provide emotional support, comfort, therapy, companionship, therapeutic benefits, or to promote emotional well-being are not service animals."
http://www.ada.gov/NPRM2008/t3NPRM_federalreg.htm