You’re asking a question here that includes a hypothetical about the state of the world that may or may not ever be true. Can you explain why this is permissible but my above strategy of asking a hypothetical regarding language was invalid?
In both cases we’re saying to the dogs "Imagine a hypothetical world where in the future a specific event has happened (i.e. “you flipped the coin a certain way” or “the dog language evolved to treat certain words differently[1]”). These future events aren’t impossible but there’s also no guarantee that they will ever happen. There’s no finite amount of time or flips that will ensure you flip heads or change your language.
Alternatively (if you don’t buy the above), the suggestion “If I asked you again and again until…” is describing a sequence of events that might never stop. So how do you ask a question about something that comes after a potentially infinite sequence? It’s like asking someone what the unreachable code under an infinite loop will do when it’s run. (And if you say that you’ll amend the hypothetical to be “Suppose you flipped the coin the same way” without reference to attempting in a sequence, then I think you are making my argument above stronger)
[1] This isn’t the original sense in which I meant my suggestion. I did mean macro substitution at that time, but I’m trying to cast that in a new light here.