A dog with a torn cruciate ligament doesn't write "pain score 8/10" on an intake form. Instead, it exhibits ethological markers : tucked elbows, reluctance to shift weight, a subtle change in sleep posture, or sudden aggression when palpated. Veterinary science is learning that nociception (the nerve signal) is not the same as suffering (the behavioral response) . A cat with dental disease doesn't cry; it stops grooming. A horse with gastric ulcers doesn't limp; it pins its ears when cinched.