"Wei Ying and I extracted his nephew from the walls of one of the castles." And not a moment too soon. "He had acquired a curse mark from within them. When I left in pursuit of Nie Huaisang, Wei Ying took the curse mark onto himself." Lan Wangji says this part just a little darkly, the way he can never be entirely unruffled about anything that involves Wei Ying sacrificing himself for another. "The arm in our possession reacted violently to the mark. We surmised that Wei Ying's nephew must have been in the presence of the arm's corresponding leg."