What does this mean? "I looked down at sohrab. One corner of his mouth had curled up just so. A smile. Lopsided. Hardly there. But there."?

These are Amir's final words about Sohrab. As they fly their kite in America, Amir notices a smile (or the beginnings of one) from Sohrab. It means there is hope that the boy may come out of his silence and embrace life once again.