Dog in murder scene and scene where Sikes is about to drown him

Just watched this brilliant film, but am upset to see the dog so frightened, especially when he is called by Newton (playing Sikes) to come towards him to be drowned, The dog is shivering and licking his lips, all genuine signs of deep distress in an animal. Can anyone help by telling me how this reaction by the dog was got? I really hope it was by good means and not by genuinely terrifying him?