This kind of thing happens a lot. Everyone around here knows somebody that knows somebody who got into a hunting/fishing/trapping accident with a dog. I have heard of duck hunters who's dogs have tripped over a gun in a boat accidentally shooting them etc.
I've heard of that happening more than once, where the gun is leaning up against a tree or something and the dog knocks into it and somehow shooting someone. Gosh! Hunters beware of your dog!
You maybe right. A dog is also an animal and he won't feel happy to see other animals being shot by his owner. He could be thinking, "I am the next" when he decided to shoot his owner.
