That's what I thought....what would happen if an actual person tried to grab his bone? That dog is mean.
Not mean ~ he is a resource guarder. Its a common behavior in dogs who have gone hungry or have been neglected (not saying this dog was.. just that you see it more in neglect cases)
It is one of the more dangerous behaviors a dog can develop and takes a ton of time and dedication to change the behavior. I have seen it done ..some people think these dogs are unfixable which is not the case but the amount of time and dedication is ..well lets just say A LOT
Most shelters along with the ASPCA usually put to sleep dogs that have this type of behavior as to not risk new parents. Its usually a death sentence to the dog unless someone who knows what they are doing and is willing to take the time with it steps in.
This type of behavior is one of the main family dog "flipped out" and bit little johnny. Its all fun and games until a kid has a scar from his eye to his chin and is forever scared of dogs.