Dominoes are the small, rectangular tiles used in a variety of games. Some people like to line them up in long rows and then knock them down. Others use them to make patterns. Still others play with them for hours at a time, making complex designs and then toppling them all over again. Whatever the game, domino is a perfect example of a chain reaction: One thing triggers another, and then that next thing triggers yet more. This is why the word domino comes to mean a sequence of events with increasingly serious–and sometimes catastrophic–consequences. Today’s Wonder of the Day was inspired by Juan, who wanted to know more about how a domino effect works.

Dominoes may be made from a number of different materials, including ivory, bone, silver lip ocean pearl oyster shell (mother-of-pearl or MOP), or dark hardwood such as ebony, with contrasting black or white pips. A set is most often made up of 28 tiles. Each tile has a matching end that fits into the other tile on the table. The ends of a domino can be either square or pointed, but the points must be touching to form a chain.

In a domino game, each player takes turns adding a tile to the chain. The first player places a tile with its matching end against an adjacent end of an existing domino. If the tile being added has more pips than the previous domino, it is called a spinner. If the new tile is a spinner, then the other end of the chain is re-counted as part of the total count. The other players must also be aware of this count, which is the basis for scoring in many domino games.

The next player must play a tile with the matching side against the exposed edge of a previously played domino. The next player must continue this process until the entire chain is completed. The winner is the player whose count of the free ends of the chains is lowest.

Some people build spectacular lines of dominoes, and these can be found on YouTube and at domino shows. The most famous of these is Lily Hevesh, who has built incredible setups for movies, TV shows, and even for a Katy Perry album launch.

The way a domino chain reacts is a little bit like a nerve impulse in the body. Once the triggering domino is tapped, it sends a pulse of energy down the line, and just like nerve impulses, the result is all or nothing. As a domino falls, the other tiles quickly follow suit, producing a sequence that can be as simple or complex as desired.