Such as a urinary tract infection or arthritis pain causing irritability.
Veterinary professionals now recognize that changes in behavior are often the first "symptoms" of a medical issue. Because animals cannot verbally communicate pain, their actions do the talking:
One of the most critical applications of behavior science is within the clinic walls themselves. Veterinary visits are inherently stressful: a stranger touches the animal in sensitive places, the smell of disinfectant is overpowering, and other animals are visible.