Okay, but what I keep coming back to is that all this 'no answer', 'no correct answer' and 'I can't tell you' stuff still isn't OBVIOUS. It's supposed to be something that once you see you can't unsee (Derek). Iam, I like your explanation, but it still doesn't seem like something that you'd be positive of once you figured out, especially if you figured it out on your own just by thinking (as opposed to in coversation with someone else). Also doesn't quite match with a friend (relative?) who got half of it and was led to the rest. Also, like "BlockRock"'s post, it also has nothing to do with the words of the joke itself. So how could it possibly be obvious and possible be semantic?
So, and I have read all the posts (except perhaps any I'm cross posting on righ tnow :) ) although I may have skimmed some, I'm going back to Derek's comment about it being semantic, and "Bloody"'s about it being existential - a word people haven't looked at semantically so far is "once". Could it be more than just "once upon a time" thing, and instead be, like, literally, once. One-time-only. Meaning that it somehow only exists once, which is why we can't talk about it anymore once it's gotten? It's now gone. It was once, and if you talk about it, it's now twice (or tenth or thousandth), and thus not correct anymore?