Mrs. Bennet has just finished relating the fact that Jane once had a suitor so smitten with her that he "wrote some verses on her".

"And so ended his affection," said Elizabeth impatiently.

Why "impatiently"? At first I thought Lizzy was just trying to shut Mrs. Bennet up. But then why not simply attempt a change in subject? Instead she goes on:

"There has been many a one, I fancy, overcome in the same way. I wonder who first discovered the efficacy of poetry in driving away love!"

Is Lizzy actually trying to subtly let Bingley, a listener to this conversation, know that Jane has no remaining ties to this former suitor?

"I have been used to consider poetry as the food of love," said Darcy.

Is he teasing her for her efforts?

"Of a fine, stout, healthy love it may. Everything nourishes what is strong already. But if it be only a slight, thin sort of inclination, I am convinced that one good sonnet will starve it entirely away."

Darcy only smiled

He's on to her!