What are some examples of behavioral compulsions in animals? How do OCD behaviors in cats and dogs stem from normal, adaptive behaviors and responses?

One example of obsessive-compulsive behavior in cats is chewing off their fur. This behavior is associated with cleaning themselves, which cats do by licking, and removing irritants such as thorns from the skin, which they do by biting. Common manifestations of OCD in dogs include chasing their tails and carrying a toy. Such behaviors become disorders when they are repeated frequently and in unusual contexts. Conflict and stress are among the causes or triggers for such behaviors. A behavior that usually relieves a small amount of stress will be repeated and extended when the animal experiences higher levels of stress. If a dog has a favorite toy, for example, in a high-stress situation, they might carry the toy constantly. Such behaviors can become problematic if the animal harms themselves, such as by chewing, or becomes resentful and even violent, such as when a human or another animal tries to take away the toy.
https://www.petmd.com/dog/behavior/evr_dog_behavior_compulsive_disorder