Domino is a small, flat, thumb-sized rectangular block with one side bearing from one to six pips or dots. A domino set consists of 28 such pieces. Dominos are used for a variety of games. They are usually stacked on end in long lines. When the first domino is tipped over, it triggers a chain reaction that causes the rest of the line to topple, and so on. This gives rise to the phrase “domino effect,” which describes a series of events that start small but ultimately have much greater–and sometimes devastating–consequences.
Almost any game can be played with dominoes. The most common types of games involve blocking and scoring. In these, each player places a tile edge to edge against another such that the adjacent edges match or form some specified total. Some games use the same basic set of tiles, while others require different sets with a different number of tiles and a different arrangement of pips on each tile.
Some games are more involved than others. For example, the game Concentration requires a single domino to have a certain number of matching sides in order to be considered complete. In other games, each player tries to form a pattern with the tiles he holds and then plays them to create a line of matches. The resulting line is called the dominoes’ layout, string, or line of play. Each player tries to position his tiles so that each open end of the dominoes is a match for the opposite-sided opening of an adjacent tile.
When a double is played, the matching ends must be adjacent. Normally, both halves of the double are counted as ends, but a special type of domino called a spinner may have its matching ends on either side. The type of end on each matching side is determined by the rules of the specific domino game being played.
The layout, string, or line of play is important because it provides a guideline for how to play the remaining tiles in the hand. If the player does not have a double, for instance, the next highest double is used to begin the chain of play. The player may also choose to place a tile with an open end on one of the four corners of the domino instead of placing it against an adjacent open end, in which case that open end is considered an end.
As the dominoes are played, a domino chain forms that develops in a snake-like shape. This chain is useful to the player because it allows him to advance his tiles more quickly and may lead to a higher score. The chain is also important because it demonstrates that the sequence of events in a domino game is similar to that of the transmission of a pulse from one neuron to the next in the body. The pulse moves at a constant speed, does not lose energy as it travels, and can only go in one direction.