A sudden onset of defensive aggression in a normally gentle dog often points to localized pain, such as osteoarthritis, dental disease, or spinal discomfort.

Cats that stop using their litter box are frequently reacting to the pain of Feline Lower Urinary Tract Disease (FLUTD) or the mobility challenges of arthritis, rather than acting out out of "spite."

Veterinary behaviorists are specialized veterinarians who diagnose and treat complex behavioral disorders using a combination of behavior modification therapy and psychotropic medications. Core Principles of Animal Learning

Sudden aggression is frequently triggered by pain. Dental disease, spinal injuries, and ear infections can make an animal lash out when touched.

Behavioral assessments in shelters have evolved: