The sky splits, and the wind and the snow blow through the holes.
Song Mo, worried for the safety of his people - the Miu, sets out to find a way to mend the sky.
He gets help from the Old Man with the long green beard and eventually manages to steal from the Wu Lung brothers their dragons' horns and dragons' teeth. The horns he uses as a hammer, and the teeth as nails, to mend the splits in the sky.
It is those nails we see shining in the sky at night.