Investigations of each behaviour, whether or not it seems abnormal, makes it easier to understand the response in terms of its causes and effects and consequently it's implications for animal welfare, and how to treat it if required. First, its performance harms the performer or other animals. Second, it can be a response to an inadequate or noxious environment and as such an indicator of suffering. Third, it can be an adaptive or coping mechanism which reduces the impact of a poor environment. Overtly harmful behaviors are problems both for the animals and their keepers.
Captive animals can harm themselves or others in many ways.
In other species, excessive grooming, scratching or escape attempts can cause feather, fur or wool loss end lead to lesions, wounds or even broken bones. Tailbiting in pigs and featherpecking in hens can wound or even kill the recipient, whereas mass movement of poultry in large, deep litter housing can lead to trampling and suffocation. Oral stereotypes in horses such as windsucking and cribbiting are irregularly associated with teethwear threatening colic. Locomotor stereotypes such as weaving and boxwalking in horses have been related to poor condition, feed wastage and lack of thrift, though again the problem maybe overstestimated as detectable losses of athletic condition are only found in high performance horses. Good evidence for apparently abnormal indicating poor welfare has been found in both motivational and physiological studies.