This is another one of those what if scenarios that could play itself out in so many ways, but after reading the cat killer posts, and then some older posts about using your firearm to put down a pet I've been thinking about this:
If you were to discover someone killing your family pet, would you legally have the right to neutralize the threat? We're talking about an armed individual, whether with a blade or a firearm, attempting to kill your beloved family pet on your property. At the time you catch him in the act, it's only aimed at the animal, would this still be considered a deadly threat if it's not aimed at you currently or would you have to wait for him to turn his attention to you before you would have the right to defend?
I think in this situation, I would be hard pressed to not think of my german shepherd as part of my family, but I know the law would not think of it that way.
If you want a more direct example, let's look at this scenario:
You are coming home from work in the late afternoon or early evening, and spot someone dressed in all black on your front yard with their back to you, you notice a large knife in his right hand stained with blood. After a quick glance, you look downward and see your cat laying on the ground, covered in blood and struggling to breath. At this point, the guy has not noticed you yet. How would you handle it?