John Thorpe asks Catherine to marry her without her realizing it, and her innocent answer is spot-on.
John Thorpe: Did you ever hear the old song 'Going to One Wedding Brings on Another?' I say, you will come to Belle's wedding, I hope. (...) And then you know, I say, then you know, we may try the truth of this same old song.
Catherine: May we? But I never sing.