providing tips to survive a zombie invasion as a "fun new way of teaching the importance of emergency preparedness". The CDC used the metaphor of a zombie apocalypse to illustrate the value of laying in water, food, medical supplies, and other necessities in preparation for any and all potential disasters, be they hurricanes, earthquakes, tornadoes, floods, or hordes of zombies. In 2011, the U.S. Department of Defense drafted CONPLAN 8888, a training exercise detailing a strategy to defend against a zombie attack. Music Michael Jackson's music video Thriller (1983), in which he dances with a troupe of zombies, has been preserved as a cultural treasure by the Library of Congress' National Film Registry. Many instances of pop culture media have paid tribute to this video, including a gathering of 14,000 university students dressed as zombies in Mexico City, and 1,500 prisoners in orange jumpsuits recreating the zombie dance in a viral video. The Brooklyn hip hop trio Flatbush Zombies incorporate many tropes from zombie fiction and play on the theme of a zombie apocalypse in their music. They portray themselves as "living dead", describing their use of psychedelics such as LSD and psilocybin mushrooms as having caused them to experience ego death and rebirth. Social activism The zombie also appears as a metaphor in protest songs, symbolizing mindless adherence to authority, particularly that of law enforcement and the armed forces. Well-known examples include Fela Kuti's 1976 album Zombie and The Cranberries' 1994 single "Zombie". Organized zombie walks have been staged, either as performance art or as part of protests that parody political extremism or apathy. A variation of the zombie walk is the zombie run. Here participants do a 5 km run wearing a belt with several flag "lives". If the chasing zombies capture all of the flags, the runner becomes "infected". If he or she reaches the finish line, which may involve wide detours ahead of the zombies, then the participant is a "survivor". In either case, an appropriate participation medal is awarded. Theoretical academic studies Researchers have used theoretical zombie infections to test epidemiology modeling. One study found that all humans end up turned or dead. This is because the main epidemiological risk of zombies, besides the difficulties of neutralizing them, is that their population just keeps increasing; generations of humans merely "surviving" still have a tendency to feed zombie populations, resulting in gross outnumbering. The researchers explain