Lan Wangji is faintly surprised that Nina is asking, but he knows that it constitutes a kindness on her part. He recalls doing the same to Claudius after the truth spell and the attack of the fierce corpses. He does, however, hesitate before he answers. "I traded with young mistress Gu." He lets the silence after that fill in its own blanks. Nina has been subjected to far too much personal information from him already. She can make the leap that Gu Xiang awoke in bed with Wei Ying without him saying so.