There are instances in which an owner of a vicious animal might not be held liable for an attack by the animal. For example, if the animal owner adequately warned other people that the animal was dangerous, and took measures to keep the animal away from people, a person who ignored the owner’s warnings and was injured by the animal might not successfully sue the owner. In legal terms, the injured person’s behavior is known as “contributory negligence” or “assumption of the risk.” An injured person is contributorily negligent when he or she fails to exercise the degree of care for his or her safety that an ordinarily prudent person would exercise under similar circumstances. For example, if a person climbs over a fence and is bitten by a dog on the other side, a jury could decide not to hold the dog owner liable if they believed that a normal person would not have climbed over the wall in the first place.

An animal owner might also escape liability if the injured person “assumed the risk” of an attack by the animal. If the owner can show that the person bitten by his or her animal had actual knowledge of the risk of injury from the animal, but voluntarily exposed him or herself to that risk anyway, a court can bar the injured person from recovering damages. For example, if the owner puts up a “Beware of Dog” sign, and a person ignores this sign and gets bitten by the dog, the owner might not be responsible for that person’s injury. If the animal owner is claiming either “assumption of risk” or “contributory negligence,” however, the owner has the burden of convincing the jury of these arguments.

An animal owner can also argue that the injured person provoked the animal, and this may be a way for the owner to avoid liability. For example, if a person makes a threatening gesture toward an animal, and the animal attacks, this could negate the owner’s liability.
The relationship between the owner and the injured person can also affect the owner’s liability. For example, if the owner invites someone over to his/her property, and the invited person (known legally as an “invitee”) is injured, the owner can be held responsible if he/she did not warn the invitee of the potential danger of the dog. On the other hand, if someone is trespassing on the owner’s property, the owner will probably not be liable for animal bites sustained by the trespasser (unless the injury is intentionally caused by the owner).