Neurotransmitters like serotonin, norepinephrine, and gamma-aminobutyric acid (GABA) dictate emotional baselines. In animals suffering from generalized anxiety, separation anxiety, or severe phobias (such as noise aversion), the brain is in a constant state of fight-or-flight.
This is where ethology becomes a diagnostic instrument. Subtle behavioral shifts are often the earliest, and sometimes only, indicators of pathology. A dog that suddenly refuses to jump into the car may not be "stubborn"—it may be signaling intervertebral disc pain. A cat that stops using the litter box is rarely "spiteful"; it is often experiencing the urgency of cystitis or the discomfort of arthritic hips making the high sides of the box inaccessible.
The synergy between behavior and veterinary science extends far beyond domestic pets.