Doubles — 8-8, 3-3, and so on — are the one part of Mexican Train that trips up new players. They’re not complicated once you’ve seen them in action, and your host can switch most of this behaviour off. Here’s what happens when a double hits the table.

A double has to be covered

By default, playing a double locks the turn: it has to be covered by another matching domino before normal play carries on. Cover your own double straight away if you can.

This is a game rule called Must satisfy doubles during the game. Whoever creates the game chooses it in the setup wizard, and it’s fixed once play starts — so it’s the same for everyone at the table. If your host turned it off, a double behaves like any other domino and nothing gets locked.

If you can’t cover your own double

1. You draw from the boneyard — one domino, or until you can play, depending on the game’s settings.
2. If that doesn’t help, your train opens up and the next player has to try to cover it.
3. If they can’t either, they draw and may open their own train too — and so on until someone covers it.

Doubles and going out

By default you can’t go out — play your last domino to end the round — while an uncovered double is still sitting on the table. You’re allowed to play a double as your last domino; it just doesn’t end the round yet. You keep going: drawing while there are dominoes left, or passing automatically once the boneyard is empty.

This is a second game rule, Must satisfy doubles to go out, and it’s separate from the one above — your host can have either on or off. Both are set when the game is created; see Game rule options for the full list.

Blake’s Rule

One friendly exception. If you play a double as your last domino and the boneyard is empty, that double can never be covered — so the round simply ends and you go out. You’ll see a cheerful “You’ve invoked Blake’s rule!” message with the results.

If there are still dominoes in the boneyard, the normal rule applies and you carry on drawing.

Branching

Once a double is covered, the train can split into two branches that people play on independently. That’s the default, and it’s another game rule — Train branching on doubles — chosen at setup. Hosts who prefer something simpler can switch it off, and trains stay as a single line.