Even if you've only seen the film version of The Hunger Games, you are probably familiar with the poisonous berries called nightlock that populate the arena. Katniss identifies and collects them to use as a weapon. Towards the end of the film (and the book), Katniss and Peta threaten to eat some nightlock and kill themselves rather than allowing only one of them to live. They are also the assumed cause of Seneca Crane's death. In the book version of Mockingjay, the berries are converted into tablets and carried by the District 13 soldiers as a means of committing suicide if they're captured. This rather grim strategy is never mentioned in the film.