Newton’s principle of action and reaction certainly applies in billiard sports. But before it does, the players need to calculate an intricate network of possibilities in the silent analysis of the cool green baize. Pool and snooker are played on a table with six pockets into which the balls are potted – some in a certain order – to score points. In three-cushion or carom, which is played on a table without pockets, the cue ball has to make contact with two others plus at least three cushions before scoring through hitting the third ball. Billiard balls vary from one game to another in size and number. The cues are made of a hardwood, generally maple or ash – the latter particularly for snooker. Chalk is applied to the tip of the cue – for nearly every shot – to increase the friction coefficient. As a consequence, slippage between the cue tip and the struck ball is avoided.