here is the full excerpt for this question
There was a sudden dropping the lower part of the old man’s face, as if some heavy weight had settled therein; he shut his mouth tight, and went on harnessing the great bay mare. He hustled the collar on to her neck with a jerrk
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A boy stood before the kitchen glass combing his hair. He combed slowly and painstakingly, arranging his brown hair in a smooth hillock over his forehead. He did not seem to pay any attention to the conversation.
I believe the answer is, to develop the relationship between the old man and the boy.
The excerpt basically tell us that the old man and the boy are in an abusive relationship.
