Years ago my wife was attacked by one of our dogs. He had slept between us the night prior (and many other nights) He had alerted on some of her seizures (post heart attack brain damage) when she was having seizures...no more, with proper meds.
I happened to be in a hospital bed recovering from new knee surgery. She had returned home to take care of the dogs....feed, outside for some exercise, etc. I tried calling. No luck. Tried again. No luck. I called her mom. Her mom honked the horn long enough for him to be distracted so she could get out the back door and collapse in the back yard. Care flight to hospital.
The male dog attacked her with no warning. The only thing different was that she entered our house through the back door.
245 staples, 43 days in wound care. UPDATE...Shoulda been 43 days in the hospital; 3 months in wound care.
He was euthanized as soon as I was well enough to take him in.
I taught one semester of Mammalian Physiology for the vet department at college just prior to getting sucked in by the Navy and called on an old friend to do a post mortem on my dogs brain.
He had a pea sized tumor on his Amygdala, which is the part of all mammalian brains that has control of temper/emotions. Certainly not his fault, but ya just cant take chances.
There was no way to predict what happened.