I was reading something by John Wheeler the other day, and in it he makes a reference to a game of Twenty Questions he played that was a little unusual. (I'm actually not certain whether this ever actually happened, or if he was just using it to make a point, but no matter). He was asking one question of each person in the room, and what he found strange was that he'd ask something simple like, "Is it edible?", and the person would think for a while, and then finally say, "No." This went on until he was finally guessing actual objects and the same thing would happen. He'd ask, "Is it a cloud?" The person he asked thinks and thinks, and Wheeler can't figure out how this can be a hard question, and then the person finally says, "Yes", and the whole room breaks up into laughter.
What he discovers is that the other people hadn't actually picked a word when he left the room. Rather, they'd just agreed that anyone Wheeler asked could answer however they chose, provided that they could think of something that would satisfy the answer to the new question, as well as all the answers previously given. So they were having as hard a time as he was in figuring out what the object was. (He was using this as an example of how the properties of quantum particles are in some sense determined only when we actually try to measure the properties, rather than existing beforehand.)
In any case, entirely apart from the point he was making, this sounded amusing, and I thought folks on the BABB might be just silly enough to appreciate the game, modified to suit the forum. So, here are the rules.
1. Anyone can ask any question. All questions (except for the first traditional one) must be answerable with "yes" or "no".
2. Anyone else can answer the question, but the person answering should have something in mind that could in fact satisfy all the questions so far answered, including the current one.
3. If someone thinks that there's no way something could exist which fulfills the requirements, that person can challenge the last person who gave an answer to tell what he or she was envisioning. If that person cannot do so (within, say, a day, to allow for the vagueries of bulletin board communication), the challenger wins that round. However, if the challenged person can do so, he or she wins immediately.
4. If a question stumps everyone (that is, nobody can think of a way to answer it and still imagine something that could fulfill the requirements), the person who asked the question wins the round. Call the time limit for an answer to be posted the same one day. For the entertainment of those playing, the person who gave the last answer should announce whatever he or she was imagining.
5. Similarly, if no one is able to devise a suitable question within a day, the person who gave the last answer may announce the object envisioned, and win the round.
6. Of course, as in traditional twenty questions, someone who guesses the object wins. Since anyone who answers is always free to try to come up with something else that satisfies the criteria so far established (and is encouraged to do so, particularly early in the round!), this method of winning may be tricky. See this message for more discussion.
7. The winner begins the new round. Since the first question is traditionally "Is it animal, vegetable, or mineral?", it probably makes the most sense to begin the round be answering this question, rather than wasting the time to have someone ask it.
So, I'll start things off: the first unknown thing is Vegetable in nature. Anyone want to join me?
[edit to explicitly allow winning by actually guessing the answer and having it accepted]