I always liked this scene because it shows a rather carefree Lizzy. She is not drooling over Darcy (which I am certain he is used to all the young ladies doing). She doesn't quite care for her dance partner, and wishes to pay him no particular attentions (beyond being civil and polite). I think she is easily distracted by the events going on around her in the ballroom, too - or would much rather be thinking of them than of Darcy.