Subtle it may be, but Lan Wangji's expression is one of sincere gladness at seeing that Susan is enjoying it, given what a departure it is from the tea she knows best. "As do I." He pauses, but he has been soothed by the tea and by the flash of quiet vulnerability from Susan, and he gathers himself to speak on rather than settling into only silence. "Brewing, pouring, and serving it is considered an art form in itself in Gusu."