The largest flipping dog I've ever been close up to - and I used to be good friends with a neighbour's Great Dane.
The size of the thing, the sheer bulk, the massive head 
I like larger dog breeds, think labrador, retriever, gun dogs etc, I own a greyhound, but that was just a bit much. I can totally see how they were used to fight lions off.
My own --wussy- grey stopped in his tracks and just stared 