What is a common sign of pain in animals?

A common sign of pain in animals is reflected in changes in behavior, which can include vocalization or aggression. Animals often express discomfort or distress through alterations in their normal behavior patterns. For instance, they may vocalize more than usual or exhibit aggressive behaviors as a response to pain, which could be a protective instinct or an indication of fear.

Hiding from humans can also signify pain, but it's more commonly associated with anxiety or stress rather than a direct indication of pain itself. Increased energy levels would generally not be associated with pain; animals in discomfort are more likely to exhibit lethargy or reduced activity. Excessive grooming can sometimes indicate stress or discomfort, but it is not as universally recognized as a clear sign of pain as behavioral changes like vocalization or aggression are. Thus, the response involving changes in behavior due to pain is the most accurate and commonly acknowledged indicator.