In the beginning of the novel Hassan's harelip or cleft lip is one of his most representative features as a child, and it's one of the features Amir's refers the most in describing him. The split in Hassan's lip acts as a mark of Hassan's status in society. It signifies his poverty, which is one of the things that separates him from Amir, simply because a cleft lip indicates that and his family don't have money to fix the deformity. At the end of novel, Assef splits Amir's lip as he beats for him, leaving Amir with a permanent scar much like Hassan's. In a sense, Amir identity becomes merged with Hassan's. He learns to stand up for those he cares about as Hassan once did for him, and he becomes a father figure to Sohrab. Because of this, it also serves as a sign of Amir's redemption.