We have an eighteen month old, 100 lb, collie/retriever mix puppy named Wiley. I always check on my kids before I go to bed and last night, he was in my daughters' room sitting by her bed, on the floor in front of the full length mirror on her closet door. He seemed very much on edge and I tried to get him to come to bed with me but he wouldn't budge. I told my wife about it and she said, "and you haven't figured out what he's doing?" I said I didn't and she told me to go take another look. That's when it dawned on me that he had positioned himself there because he was guarding my daughter from the "other" dog he saw in the mirror and he wasn't about to leave her as long as that dog was there. Good dog.