Following is their dialogue:
Harry: My whole life I have never known what this song means.
Sally: I know exactly what you mean.
Harry: I mean, should old acquaintances be forgot. Does that mean we should forget old acquaintances, or does it mean if we do happen to forget them, we should remember them, which is not possible because we forgot them…..
Sally: Maybe you're just supposed to remember you forgot them, or something – anyway it's about old friends.