When you pet your dog at night, if he responds with a loud growl, then it is his way of saying ‘No.’ You must respect your dog’s decision and back off for now. Your dog could also be in pain, and if he has any injury or wound, he may let out a growl when you touch that part of his body. You should also learn to distinguish a happy growl from an angry one by looking at your dog’s body language. When your dog is happy, he gives submissive grins and plays bows. If your canine is angry, he will appear stiff and maintain a serious expression.