“For Burners, the ritual experience begins as soon as they walk through the gate, where people hug and greet each other with the phrase, ‘Welcome home!’ They refer to Black Rock City as their home and the outside as 'the default world.' That home is treated as sacred, demarcated by the straight lines of a pentagon and protected from the polluting influence of the outside world. Upon their departure, Burners must remove all Matter Out of Place (MOOP). This is a concept borrowed from the anthropologist Mary Douglas, who used it to describe how cultural notions of purity and pollution are used to designate the things society holds sacred. According to Douglas, purification rituals create symbolic boundaries that separate the domain of the sacred from that of the profane. Anything that transgresses those boundaries is seen as a source of pollution and danger, not because it is inherently unclean but because cultural norms dictate that it does not belong there. In a shopping mall, wearing shoes is considered clean while walking barefoot is unclean; in many religious temples, the opposite is true. When the transgression is unavoidable or necessary, a purification ceremony ensures that it is not harmful. For instance, a priest must perform cleansing rites before entering the altar. At the end of Burning Man, Burners conduct 'line sweeps' in order to find and remove all MOOP. Precise rules dictate the number, arrangement, distance and movement of MOOPers. Even the tiniest particles must be removed, including hair, wood splinters or glitter, and everything is meticulously documented and inspected…. Various other rituals help further demarcate the boundaries between Burning Man and the outside world.”