Jack: Actually, I was found. Lady Bracknell: Found? Jack: Uh, yes, I was in... a handbag. Lady Bracknell: A handbag? Jack: Yes, it was... [makes gestures] Jack: an ordinary handbag.
Just as the orator marks his good things by a dramatic pause, or by raising and lowering his voice, or by gesture, so the writer marks his epigrams with italics, setting the little gem, so to speak, like a jeweler.