This liability does not preclude all common law defenses. Thus dog owner may raise the defense of assumption of risk or willfully invited injury. This type of defense is typically available is where the alleged victim was attacked after trying to hurt or taunt the dog. Also, if a person knows and and appreciates the danger involved in encountering an animal such as a hostile and barking dog, and voluntarily accepts the risk by exposing himself to the hazard, the injured person may had difficulty winning his case.
The defense of assumption of the risk extends only to the danger that the injured person has knowingly assumed. The dog owner would generally not be relieved of liability of the victim's injuries, if he purposefully or negligently concealed a particular hazard, since this would expose the injured person to an unknown risk. Thus, a dog's prior history of vicious behavior and the dog's owners of that behavior is highly relevant and often critical in winning a dog bit injury case.