I would argue that the leash or collar breaking IS negligence, not an accident. I believe a pet owner is responsible for ensuring their gear is up to the task.
If the gear fails to work as intended and the animal/weapon gets out of control and kills something, how is that any different than a bullet that ricochets beyond the shooter's intended path and killing something? Both events should carry the same responsibility.
If the gear fails to work as intended and the animal/weapon gets out of control and kills something, how is that any different than a bullet that ricochets beyond the shooter's intended path and killing something? Both events should carry the same responsibility.