"As far as "snapping" goes, humans are good at it. Especially when they feel threatened."
I agree. In fact, I think it's safe to say the only animals that "snap" ARE humans. Animals do a pretty good job showing what they like and dislike, if you know how to read them. People carry things with them until they get unbearable. Dogs seem to be pretty cause-and-effect kind of creatures, and they definitely don't have any natural reason to hide their "emotions" until the boiling point.
I read somewhere recently that every year people are bitten more often by other people than by dogs.
Not all dogs are honest, though:-) I have a lab ornery enough to command all the tennis balls in the yard. What can I say? He's smarter and quicker than the females, but not a bit more lovable.
As for intelligence and quickness, I did have a female Pitbull that would run rings around him. She was the best dog I've ever known.