The “one bite” rule has its roots in English common law. In earlier times, the law allowed a domestic animal to bite its first victim without consequences. Today, this is not necessarily the case. A dog owner is no longer allowed one “free dog bite” if it can be shown that the owner knew or should have known that the dog had dangerous propensities.
Proving the dog was dangerous or vicious can be tricky because there are no standard criteria. The court has discretion and will weigh available evidence. A prior bite would be strong evidence, but even showing that the dog previously acted aggressively – growling, snarling, baring its teeth at people or lunging at people – may suffice.