Eventually, the colonists realized that, even with this small army of paid rat killers, they were failing to make a dent in the rat population. They pr

Eventually, the colonists realized that, even with this small army of paid rat killers, they were failing to make a dent in the rat population. They proceeded to Plan B, offering any enterprising civilian the opportunity to get in on the hunt. A bounty was set—one cent per rat—and all you had to do to claim it was submit a rat’s tail to the municipal offices. That way, the government wouldn’t be overrun with bulky rat corpses. “I always think about that,” Dr. Vann says. “Who is the poor guy counting all these rat tails?” The Vietnamese, too, were pleased with the arrangement, but not for the same reason. In the beginning, rat-tails poured in as locals slaughtered them by the dozen. Their entrepreneurial spirit took over though, and soon enough, French health officials began to notice a strange phenomenon: tailless rats proliferating in the outskirts of the capital. Upon further investigation, it became apparent that the Vietnamese were breeding rats specifically to receive cash for their tails. Reports also suggest some people smuggled out-of-town rats into Hanoi. By 1906, there was an outbreak of plague as a result of the infected rat population. At least 263 people died, most of whom were Vietnamese. http://www.atlasobscura.com/articles/hanoi-rat-massacre-1902 http://www.atlasobscura.com/articles/hanoi-rat-massacre-1902 https://en.wikipedia.org/wiki/Cobra_effect https://en.wikipedia.org/wiki/Cobra_effect