What can you learn when a domino player passes?

When a player passes in a block game, they hold no tile carrying either number on the ends. That is certain, not a guess, and it does more than empty one hand: every unseen tile of those two numbers is now squeezed into the hands that did not pass. In a full four-player deal, one pass can turn a one-in-three guess about where a tile is into a coin flip, and two passes on the same number can tell you exactly who holds it.

How much a pass proves depends on one rule your table may or may not play: whether a player is allowed to pass, or draw, when they could have played.

When a pass is proof

Pagat.com, John McLeod's rules site, records partnership play in plain terms: players must play a tile if they legally can, and a player who cannot must pass. Under that rule a pass is a fact about the passer's hand.

Tables treat the rule seriously. The competition rules for a tournament at the Universidad de Guadalajara's Lagos campus in Mexico penalise a pase en falso (a false pass, made while holding a playable tile) by 30 points off the offender's differential, and let the wronged side choose instead to take the hand or rebuild it where possible. At a home table with no penalty, a false pass is still the one move that poisons every inference below, so it is worth calling out the first time it happens.

How the pass is shown varies too. Pagat says it is usually done by knocking the table with a tile. A 2026 rulebook for senior games run by Confa in Colombia asks the player to say paso aloud, and the 2024 rules for Bogotá's district community games forbid striking the table with tiles at any point.

Where the tiles go

The pass tells you what the passer does not hold. The useful part is the reverse: where those tiles must be instead.

Take four-player partnership dominoes, all 28 tiles dealt, seven each. Play goes from you to the opponent on your left, then your partner, then the opponent on your right. You hold:

[4-4] [4-1] [4-6] [2-2] [2-0] [3-1] [6-3]

You lead [4-4]. Ends: 4 and 4.
Left plays [4-5]. Ends: 4 and 5.
Partner plays [5-5]. Ends: 4 and 5.
Right plays [5-2]. Ends: 4 and 2.
You play [2-2]. Ends: 4 and 2.
Left passes.

Now count. The fours are [4-0] to [4-6]. Two have been played, you hold two more, so three are unseen: [4-0], [4-2] and [4-3]. The unseen twos, besides [4-2], are [2-1], [2-3] and [2-6]. Six unseen tiles carry a four or a two.

Eighteen tiles are hidden from you, six in each of the other three hands. Before the pass, any one of them was equally likely to sit with any player. After it, none of the six is with Left, so all six are split between your partner and Right.

Question	Before Left passed	After
Partner holds [4-2]	33%	50%
Partner holds none of the three unseen fours	27%	9%
Partner holds no four and no two at all	5%	0.1%

The same arithmetic applies to Right. One knock from Left has told you that both of the next two players almost certainly can play on this line, and that Left will keep knocking as long as a four or a two is showing on both ends.

Two passes on the same number

Continue the hand.

Partner plays [4-3]. Ends: 3 and 2.
Right passes.

Right holds no three and no two. Left already showed no two. So every unseen two is in your partner's hand: [4-2], [2-1], [2-3] and [2-6]. Partner has five tiles left, and you now know four of them.

That is the most valuable position a pass can give you. The two end belongs to your team. Neither opponent can ever play on it, and your partner has four tiles that can. Whatever you do on your turn, do not play [2-0] on the two and hand the opponents a new end. Play on the three instead. [3-1] makes the ends 1 and 2; [6-3] makes them 6 and 2. In a pip-scored game, shed the heavier [6-3]. Either way the opponents now need a one or a six to stay in the hand, and your partner sits behind them holding a road nobody else can use.

Your partner's pass

When your partner knocks, the arithmetic is the same and the advice flips. The numbers on the ends are the ones your partner cannot use, so on your turn move away from them if you can. Change the end your partner is stuck on to a number they might hold.

Remember that the opponents read your partner's pass too. They now know where the tiles of those numbers are not, and a good opponent will try to keep those numbers on the board.

Draw games: what a draw proves depends on the table

In draw games the rule that makes a pass certain is not universal.

Pagat's main draw-game rules let a player draw from the boneyard even when they could play. A player who draws has proved nothing about their hand. Pagat even gives a reason to do it: to look for a tile that can block the game.
One variation on the same page, and the Puerto Rican rules it describes, make drawing illegal while you hold a playable tile. There, a player who draws held nothing for either end at that moment.
How many tiles you draw also differs. Pagat's main rules have a player draw until they play or the boneyard is down to two tiles; variations limit it to one or two tiles a turn.

Under the strict rule, count the draws. A player who draws three tiles and plays the third held nothing for those ends when the turn began. They also drew two tiles that did not fit, though you cannot see which. The pass itself only comes once drawing is over: in pagat's main rules the last two tiles stay in the boneyard, and a player who still cannot play passes. That pass is as certain as one in a block game.

When sleeping tiles blur the picture

A pass only moves tiles into other hands if no tiles are left out of play.

In two-player block with seven tiles each, 14 tiles sleep. If your opponent passes, every unseen tile of the two end numbers is sleeping, and in a block game nobody draws. Your opponent cannot play on those numbers for the rest of the hand. Keep one of them on the line and your opponent can only ever play on the other end.

In pagat's four-player block game, five tiles each, eight tiles sleep. After a pass, an unseen four could be in two hands or in the sleeping pile. The chance your partner holds a particular one rises only from 22% to 28%. The pass is still certain about the passer; it just tells you less about everyone else.

The guide to probability at the table covers sleeping tiles in more detail.

Making a player pass, and scoring for it

In most traditions forcing an opponent to pass wins you nothing directly. It costs them a turn and often decides who goes out first or who is lighter if the hand blocks.

Some tables pay for it outright. Pagat records a Puerto Rican partnership game, Doscientos, in which some players give 20 points to the team whose tile first makes the next player pass in a match, and 10 points each time after that. Two passes in a row score only once. A three-pass block pays the player of the last tile 20 points, 10 for each opponent who passed. Ask before the first hand whether your table plays this, because it changes how hard you hunt a pass.

The article on blocked games covers what happens when all four players knock.

Not giving it away yourself

You cannot hide a pass. If you have no tile for either end, you knock, and the whole table learns the same facts about you. What you can do is make passing less likely and less informative.

Keep numbers, not just tiles. Before you play, check which numbers you can still answer afterwards. Spending your last tile of a number while it is showing on the other end is how good hands end up knocking.
Watch what your play leaves. Your new end is a number the next opponent must answer. If they knock on it, you have learned something. If you knock on it later, they have.
Know what your speed says. In Jamaican partner play, as pagat records it, talk and gestures about your tiles are forbidden, but hesitating or playing at once is fair to read. A long pause before a single forced play tells the table you had a choice when you did not.

Something to try tonight

Every time someone knocks, say the two numbers to yourself and the name of the player who knocked. Then count how many tiles of each number are still unseen. When a second player knocks on the same number, work out who holds the rest. The first time you know four of your partner's tiles without being told, you will play the hand differently.

The guide to what separates a good player from a lucky one shows how counting and reading passes fit together.