We sometimes forget that dogs are just animals - we assume that they are special, with human values and human reactions. They aren't.
My uncle had an Alsatian many years ago. As Alsatians go, it was a big one, it was his constant companion for about 5 years. It watched as he was hacked to death with a machete. With hindsight, it would probably have been better if it hadn't been chained up at the time, and had died trying to save him. Unsurprisingly, my Aunt clung to the dog, and brought it back to the UK, where it lived with her for a time in a two bed bungalow. In reality, it was far too much dog for her, it was a big softy, but it was used to a space of several thousand acres, and she realised that a small garden wasn't really fair on it. So it was put up for rehoming, and some suitable owners were found, they were fully apprised of the dog's history. All was good for several months, until the owner's wife decided to pull a blanket over the sleeping dog one cold night. God knows what the dog was thinking about, but it instantly woke in "you're killing my owner with a machete" mode, and went for her throat, big time. Lots of blood and hospital. The dog was completely nuts at that point, and was destroyed on the spot.
The line between cuddly family pet and 8 stone predator can be very thin at times.