I have special memories of playing dominoes every weekend with Dogfood Bob & his wife, Gloria. Just recently, I taught Fisherman Willie's wife, Sue, to play. The dominoes go from 6 down to blanks. You begin the game by each drawing 7 dominoes. You play 7 rounds, beginning first with the double 6 domino. You can't play any other dominoes until that double 6 is played. Sometimes we end up pulling all the dominoes from the drawing pile until at last! There it is. So you start with 6 & each round begin with the next number below; 6, 5, 4, etc.
When a double is played, it's call "Chicken Foot." And you have to have a domino with that number on it. You need a total of 3 (like a chicken foot) before you can play other dominoes. So we started the game, and played all the way . . .
Notice what's wrong, here? We played until Sue pulled the double 6 domino and realized that we'd played the 6's against the double FIVE domino. And neither one of us realized it! :-) Good times!