How does the mirror treatment play a significant role and how does it affect the story?

Dave's punishments began to evolve. It started with having to sit in a corner of the bedroom, and progressed to the "mirror treatment," in which she would smash his face against the mirror and force him to say he was a bad boy. When their father was away at work, she would have Dave and his brothers search the house for something she lost. These searches continued until Dave was the only one doing them, and she would beat him when he asked what they were looking for. He never found any of the things for which he was supposedly looking.