If you could make your pet understand one thing, what would it be?
Animals get more from our tone of voice and body language than our actual words. They observe our physical clues to determine what we want them to do. They watch our facial expressions, our posture and body movements. They listen to the tone of our voices.
Dogs are pretty in tune to their surroundings. So if we want them to know anything they would know from our actions not our words.
From Pity to Praise 