The Suicide Tree or Cerbera odollam works by disrupting the heart's natural rhythm, often causing death. A member of the same family as the Oleander, it used to be used for "trial by ordeal" in Madagascar. It's estimated that 3,000 people a year died from ingesting Cerbera poison before trial by poison was outlawed in 1861. (If you survived, you were innocent. If you died it didn't matter because you were dead.)