Learn to identify a "lip lick" (unless food is present) or a "whale eye" (showing the white of the sclera). These are early warning signs of anxiety. If you see a freeze response, stop the procedure. Give the animal 60 seconds in a low-stimulus environment (turn off overhead lights, remove the offending tool). Resetting the emotional state prevents learned helplessness.
One famous case study involved a normally docile Golden Retriever who suddenly attacked its owner. A veterinary behaviorist ran a bile acids test and discovered a portosystemic shunt (a liver defect). The liver wasn’t filtering toxins, which were accumulating in the brain, causing hepatic encephalopathy and aggression. The dog didn’t need a trainer—it needed surgery. zooskool stray x dog