 FACT: In the lighthouse, Yuko Sakaki accidentally poisons Yuka  Nakagawa with powder from a bottle labeled "KCN" (potassium  cyanide). About 10 seconds later, Yuka vomits blood (which suggests  internal bleeding) and dies. Cyanide is actually a poison that shuts  down the respiration in cells. Ingestion of more than 50mg of  cyanide will result in rapid respirations, loss of consciousness,  convulsions, gasping, and death due to cessation of respiration.