Dogs are masters in reading body language. Take for example you come home and smell poop. Before you ever open your mouth you lift your torso, turn your head. The dog, seeing this change, understands immediately that something is wrong. You now look at the dog. The dog sees the aggression is directed towards it and reacts accordingly. So far, you haven't said a word and all body movements are almost involuntary and imperceptable but your dog just read you like a book. He has no way of knowing why you are acting this way. You go towards the smell and your body language increases. The dog reacts by becoming more unsure - read by humans as guilt - but is only a reaction to you, not the cause of you behaving this way. Yelling at the dog at this point is an exercise in teaching the dog to mistrust you. You blow hot and cold it seems. Just watch a dog that is "adjusted" to sit the correct way on a previously good recall exercise. It takes no time at all for it to start slink half way to you with trepidation. I see so many dogs get this way during the teaching of the drop on recall. Your body says come and your actions say beware.