Genetically altered wasps that are coded to attack anyone or anything that disturbs their living. When they make that person a target, they will follow their target until they are stung. Stings from the tracker jacker are extremely painful and cause serious hallucinations. In extreme cases, it cause death. Tracker jacker venom can also be used to hijack a person's memories. The venom creates hallucinations upon the memory and the memory is then seen differently by the person. From The Hunger Games

the thing that you don’t have when you’re phones percentage is over 20