Horror!
The Harvard Gazette discusses why people are attracted to horror movies, and the sociocultural forces that have shaped the genre over the years.
Although few ads (actually, none that come to mind) draw on horror to engage consumers, this article is relevant for marketers because ads (like movies) are ways of testing out anticipated experiences.
Note the reference to the Centers for Disease Control zombie handbook. Although the CDC is still determining whether this actually has influenced people to prepare for real emergencies, the metaphor of "hurricane/tornado as zombie attack" drove record traffic to the CDC disaster preparedness site.