What is a common sign of pain in animals that may require analgesia?

Lethargy is a common sign of pain in animals and can indicate that an animal is not feeling well or is experiencing discomfort. When an animal is in pain, it may become less active, choosing to rest rather than engage in normal behaviors. This withdrawal from activity is a natural response to pain, as the animal may instinctively seek to limit movement to avoid exacerbating their discomfort.

Increased appetite, excessive grooming, and panting can be related to various other conditions or stressors and are not as clear indicators of pain. For instance, an increase in appetite might signify improvement in health or even stress, while excessive grooming can sometimes be a response to anxiety or skin irritations rather than pain. Panting is often associated with overheating or anxiety rather than pain specifically. Thus, lethargy stands out as a more definitive indicator that the animal may require analgesia to manage underlying pain.