I agree DeborahAnn. Perhaps for the first time, Darcy is captivated by a woman (Lizzie) who is not interacting with him for the motivation of attracting him as a husband. She, apart from her "fine eyes" and a growing recognition of her other physical assets, stimulates his mind like no-one else, and he loves it! At this point, Lizzie is only sparring with him because she enjoys it and not because of any attraction on her part. Caroline is so calculating in everything she does and says that there is nothing authentic or real about her - it's all contrived, in her mind, as making herself attractive to Darcy. Her malice makes me cringe!