I remember my dog back in the 80's running away from me when I called her and I was mad at her. Every dog since, I've made a point TO call them in angry voices and when they come, praise them - since they did just obey. They get the picture pretty quick. It's harder for people, I think, to switch gears quickly from anger to praise, but when the dog can do this, it sure beats having them run into traffic or something dangerous to get away from a mad human!