It takes very little to kill you if explosives are placed inside your body.
A cortex bomb is a small bomb, placed near the heart or cerebral cortex where even a small concussion can kill you. If the right stimuli, such as an encoded radio signal or a set time limit expires, the bomb explodes, forcing you to make a Death Test with a difficulty of 25. A BehaviorChip can be given control over the Cortex Bomb, a particularily nasty situation.
Placing the bomb near the heart instead of in the cortex reduces the difficulty of the Death Test to 20, but makes the death look like a natural heart attack to all but an autopsy.