A large portion of Karakuri Island was blown up by an explosion caused by Franky, who activated the self-destruct switch in Vegapunk's laboratory. Although Kitton's grandfather warned him about it, Franky mistook the button's skull and crossbones design for a pirate symbol and pressed it, causing the whole lab to explode. News of the incident swiftly spread around the world and the event was dubbed "The Nightmare of Barujimoa".
This is the second time a "danger" skull and crossbones was mistaken for a jolly roger, the first being when Chopper went to look for the poisonous Amiudake mushroom. Interestingly, both instances involved a doctor of one profession or another, and both occurred on Winter Islands.