Nightlock is a wild plant with extremely poisonous berries. Katniss first heard about this plant from her father, who cautioned her that anyone who ate nightlock would be dead before the berries even reached their stomach. Although this phrasing may be an exaggeration, the plant's effects are indisputable: Foxface indeed died very quickly after consuming nightlock. The only known sources for these deadly berries are the land around Districts 12 and 13, though they were also featured in the arena of the 74th Hunger Games.
74th Hunger Games
Foxface, the female tribute from District 5, stole nightlock berries that Peeta had gathered, and died after consuming them. Peeta himself had mistaken them for edible berries (possibly the blueberry-like berries that Rue had shown Katniss when they had formed an alliance). Katniss stopped him from eating any, remembering her father's warning, though she and Peeta kept some in a bag in case they could trick Cato into eating them. On the last morning of the Games, after Cato had been killed by the wolf-mutts, the previous rule change allowing two victors was revoked. Instead of battling against Peeta, however, Katniss pulled out the nightlock berries, which she and Peeta threatened to consume and leave the games with no victor at all. Before they could swallow them, Claudius Templesmith took back the change, and are both were announced as victors of the 74th annual Hunger Games. This scene was not included in the Capitol's 3-hour long recap of the Games, as it was a sign of "rebellion".
Head Gamemaker Seneca Crane later loses his life for allowing both Katniss and Peeta to emerge as victors. His specific manner of death is never explained in the novels, though near the end of The Hunger Games film, he is locked in a room containing only a bowl of nightlock berries. The shot ends before anything else happens, though the implications are clear. This cruel twist was likely ordered by President Snow.
During the Second Rebellion, soldiers from District 13, including Katniss herself, were given specifically formulated poison capsules to swallow in the event they were captured. Dubbed "nightlock", they were known to have the same effect as the berries themselves.
Nightlock was also the keyword for the Holo used by Squad 451 during their infiltration of the Capitol. When said three times in a row, the word caused the Holo to self-destruct, killing everyone within a 10-foot radius.
Real plants similar to nightlock
The name "nightlock" is derived from two real-life plants: Deadly Nightshade (Atropa Belladonna) and Hemlock (Conium Maculatum), both of which are extremely poisonous (though the Solanaceae family, which includes Deadly Nightshade, also includes many edible plants such as tomatoes, potatoes, and chili peppers, and the Apiaceae family includes carrots as well as hemlock). Deadly nightshade berries are similar in appearance to nightlock, and both nightlock and real-life hemlock are commonly mistaken for edible plants—nightlock for Rue's berries and hemlock for wild carrots. Seneca Crane's execution by nightlock berries in the film is reminiscent of Socrates' execution by hemlock, after he was tried for "corrupting the youth" of Athens, as well as "questioning the gods".
- Nightlock is said to look like an edible type of berry Rue had found in the arena, which may be blueberries, since they fit the same description.
- In the making of the first movie, the stylists were said to be annoyed with the berries, as they stained the actors' clothing.