I. The story
The snow was blowing, the hot cocoa was warm, and I had just settled down for the night with my friend Alice's family to play a holiday game or two before going home to my own family for Christmas. To my surprise, however, instead of us all playing a friendly game of Codenames, Taboo or Yahtzee, I was let in on a holiday secret.
"Every year," Alice explained, "we play a secret holiday game. It's a Christmas-themed variation of a well-known game that anyone can play, but nobody outside of our family is allowed to know the rules we use, how to play, or how to determine the winner and loser. It's our Christmas secret."
"We'll play one round of the game for you, and give you a chance to learn it from listening to us play," her brother, Bob, added. "Both of us won't necessarily play perfectly, but we'll be playing strategically to try and stop the other from winning. You don't need any other information except for the words we say out loud, although a piece of paper and a pencil could help keep track. Then we'll play a second round of the game, and if you can figure out what the game is from there, you'll get to be part of the secret from now on."
"You're on," I said, confident in my puzzling abilities.
II. The game
The first round of the game played out as follows.
- Alice: "Jingle bells."
- Bob: "I saw Mommy kissing Santa Claus."
- Alice: "Rudolph the red-nosed reindeer."
- Bob: "I can’t let you win next turn, so... Feliz Navidad."
- Alice: "Grinch."
- Bob: "Oh, drat, that was clever. I would have said Joy To The World next to stop you, but I can't. You've also already taken what I would need to win."
- Alice: "If you can't go, then I win by default!"
The game was now over. They then began the second game.
- Alice: "I'll start out differently this time. Hark the herald angels sing."
- Bob: "In the bleak midwinter."
- Alice: "Coventry carol."
- Bob: "Oh, no you don't. Silent night."
- Alice: "Drat, now I can't win. Whichever one I say, you'll take the other one!"
The moment she said that, I suddenly realized what the game was! After declaring my newfound knowledge, I was officially entrusted with the Christmas secret. Now you have to do the same.
What is the name of the game Alice and Bob were playing, and what are the rules? A complete answer will also explain the logic of their moves, the conditions of victory and defeat, and their comments each turn.
(Note for clarity: Punctuation and capitalization are not important, only the words themselves.)
"What did you mean about a paper and pencil being helpful, Bob?" I asked curiously, as we made a fresh batch of hot cocoa afterwards.
"Well, it'll help keep track of the score, and if anybody goes over," he said. "But if you get the rules, you could just as easily keep score in your head. And if you really want to game the game, you could draw a specific thing to help you strategically know what to say."