pain in animals pain in animals pain negatively affects the health and welfare of animals. "pain" is defined by the international association for the study of pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." only the animal experiencing the pain can know the pain's quality and intensity, and the degree of suffering. it is harder, if even possible, for an observer to know whether an emotional experience has occurred, especially if the sufferer cannot communicate. therefore, this concept is often excluded in definitions of pain in animals, such as that provided by zimmerman: "an aversive sensory experience caused by actual or potential injury that elicits protective motor and vegetative reactions, results in learned avoidance and may modify species-specific behaviour, including social behaviour." nonhuman animals cannot report their feelings to language-using humans in the same manner as human communication, but observation of their behaviour provides a reasonable indication as to the extent of their pain. just as with doctors and medics who sometimes share no common language with their patients, the indicators of pain can still be understood.