Placing dominoes next to each other in a line is the most classic way of preparing a chain reaction. The choice of distance between dominoes is crucial for ensuring an appropriate toppling behavior. On the one hand, if dominoes are too far apart, they will not touch each other when the first one is toppled. On the other hand, if they are too close to each other, they merge into a block that might be too bulky to topple. In professional toppling projects, it has become good practice to keep the distance of another imagined domino between two adjacent pieces.