Assassin Implant
Typically meant to be injested along with liquid or food, less than a tenth of a gram and the size of the end of a grain of rice,this highly illegal device is made of a military-grade memory plastic that is keyed to respond to a human beings core body temperature. When that temperature is reached, the highly-compacted grain undergoes a series of violent ossilating expansions and contractions, elongating from it's normal form to a foot-long hollow needle as the tightly-coiled filiments 'unwind', their potential energy discharging. Usually this happens when the grain is in the lower abdomen, peircing the intestine several times before the pellet's fillaments discharge and the whole thing disintergrates.
More expensive models grow microscopic hooks to lodge in the throat, then uindergo the ossilation process, attempting to hit the heart.