Get a group of people together. Choose someone to start. Whoever starts chooses any word they want but it has to be a word from a Christmas carol, and the other players have to think of a carol that has that word in it. Whoever gets it first, then it's their turn to choose a word. It's not as easy as you think...your mind actually goes blank. Now if the group never heard the song before, they will ask you "I challenge you", and that person has to sing a piece of the carol. (just so that they know the person isn't making it up. Or maybe they are! It's really fun!