Generally in response to their situations. Turn invisible if frightened, blast with fireball if furious, start to spark if happy. But even the last could be dreadfully embarrassing.
At least. There is the problem that people with magic that can lash out tend to be very uncomfortable to be around. Adventuring is not exactly an option.
Meanwhile, I've still got to roll my own bloodlines. Three of them. Such is the will of the story.