My Mom was bitten by a Lab. Still has nerve impairment in her left hand.
The dog belonged to my paternal grandfather. For whatever reason, the dog was allowed to live to it's natural end.
That is hard for me to believe. My black Lab has never even taken a snort at anyone. He is 120 lbs and lets some of my small nieces and nephews tug at his ears. He likes the attention.
I always have a rule of thumb with biting dogs.
One time, shame on the dog, twice shame on me. Dogs don't have hands or a voice, so they communicate fear or loathing with their teeth or mouth. Those that bite hard and draw blood without provocation however, must be watched closely and effort must be made to retrain. If it bites again, I quietly and without hesitation, kill them.