Broom, D. M. 2019. Abnormal behavior and the self-regulation of motivational state. Journal of Veterinary Behavior 29, 1-3.
Although most abnormal behaviors, including all stereotypies, indicate poor welfare, some that occur in rare situations are functional and do not indicate a negative situation. There is a wide range of abnormal behaviors that occur in conditions where the animal's needs are not met, and these can be valuable welfare indicators, but these should never be called “vices”. Some behaviors, both normal and abnormal, can be used as motivation-modifying methods. Such behaviors affect subsequent behavior and physiology, including feelings and emotions. The feelings and emotions in turn affect future behavior. Such complex mechanisms are a part of the regulatory functioning of sentient animals. The existence of these mechanisms helps to explain some abnormal behaviors and their consequences.