Zwicky, invited implicature

A. Z. online:

"They came by bearing pizza, after which event we watched The Music Man."

"(In fact, some usage writers insist that (1) is unacceptable, because which has no noun antecedent in the sentence — so that (1) is “vague” — and that something like the clunky (2) must be used instead. See the summatives posting linked to above.)
And now for a subtlety. Although (1) describes only two events, most readers will understand (1) as implicating a third event, of pizza-eating, intervening between the other two, and the author of (1) surely intended this implicature. A nice little case of how sentences can end up conveying more than they literally mean. (The sentence is true if no event of pizza-eating occurred on the occasion in question.)."