In any game, there are always two opposing sides; this is certainly the case in the area of illegal immigration.
In the book, Urrea discusses how the Border Patrol agents (La Migra) often find themselves at odds with the Coyotes (human smugglers) who facilitate the migration of illegals across the Mexican-United States border. Urrea characterizes the conflict between the Border Patrol agents and the Coyotes as a game.
While the Coyotes aim to guide their charges across the border unseen, the Border Patrol agents are paid to "see the invisible." In this daily game of cat-and-mouse, Urrea tells us that the Coyotes "score" when they successfully guide their clients across the border. On the other hand, the Border Patrol agents get to "score" when they manage to stop the Coyotes on any given day. In this dangerous "game," there is a formidable referee, and it is La Muerte (Death). Urrea describes Death as a "masked invader who regularly storms the field to disrupt the game."
With two opposing sides and a referee of sorts, illegal immigration is a game of wits at best and a vicious game of survival at worst. Both sides (as in any game) depend on trusted strategies to win the conflict. The Coyotes and their charges tape blocks of foam rubber to their shoes so as to leave no prints. They also utilize what they call the "brushout." This is when the last man in any group walks backwards and uses a branch to wipe away the footprints of those who've gone before him.
Meanwhile, the Border Patrol relies on in-ground sensors buried in places known only to agents. The agents "cut" the land (checking the sensors) in search of illegal immigrants who've lost their way; so, these agents are the "cutters" in search of "walkers" (the illegals). In their line of work, cutters know that illegal immigrants often cross the Mexican-United States border between the hours of 11pm and 3am. Thus, they scrutinize the tracks left by the migrants as they track them across the border.
Often, the agents rely on signs left by small animals that trample over the footprints just before dawn. The animals make what are known as "bug-signs." If the bug-signs cross over the footprints, Border Patrol agents know that migrants crossed nearer to midnight than to dawn. On the other hand, if the footprints appear to crush out the bug-signs, agents know that migrants may have recently crossed and are probably nearby. If so, with a new day beginning, these migrants will be in trouble once the blazing sun powers its merciless rays against their backs.
Most of time, by using the in-ground sensors, the agents are able to corral the walkers into a tight area, where they can then apprehend them. At other times, as with the Yuma 14 who perished in the desert, walkers can unwittingly wander way "off the map," where La Muerte eventually claims them for his own. So, from Urrea's point of view, illegal immigration often results in a perilous game of life and death.