Something about canines: ALL of them are territorial to some extent. Some of them just bark at anything unfamiliar that comes into their turf.
Others become violent and attack whatever unfamiliar thing is "trespassing." That's most likely what happened in this case; the Mastiff mistook the Nintendog's bark as a real bark, and since it had been sleeping in the other room it only knew that the sound came from the girl's location.
Others become violent and attack whatever unfamiliar thing is "trespassing." That's most likely what happened in this case; the Mastiff mistook the Nintendog's bark as a real bark, and since it had been sleeping in the other room it only knew that the sound came from the girl's location.