Which sign is commonly recognized as an indicator of pain in animals?

Changes in behavior, such as aggression, are often significant indicators of pain in animals. When an animal is experiencing discomfort or distress, it may react in ways that are uncharacteristic for it, such as becoming more aggressive or withdrawn. This alteration in behavior reflects the animal's struggle to cope with the pain and can be crucial for caregivers to assess the animal's well-being.

In contrast, stable weight and behavior suggest that the animal is likely not in pain, as consistency in these areas typically indicates good health. Regular activity levels and consistent vocalization also do not signify pain; instead, they can be indicators of a healthy, active animal that is not under distress. By observing behavioral changes, especially aggressive responses, caregivers can better identify when an animal may be suffering and needs medical attention.