The Great Hanoi Rat Massacre of 1902 Did Not Go as Planned (2017)

Under the streets of French Hanoi, rats multiplied exponentially—and then skittered to the surface. We only know about the rat hunt at all because in the ‘90s historian Michael Vann was in France, researching French colonialism, when he came upon a file labeled “Destruction of Animals: Rats.” In 1997, Vann went to Vietnam to do archival research on the rat massacre.

Source: www.atlasobscura.com