Bugs are robotic probes used by the Machines to track a Bluepill's location in the Matrix. They are placed onto a human subject's skin, where they will burrow underneath and take shelter inside the subject's body.
While activated they appear to be a small dark gray steel shrimp-like robot with wiry tentacles and a single red eye. However, once deactivated the squirming probe will appear to be back in a motionless steel probe and the red eye turns off.
Bugs can be removed from the host's body using an extraction device. The process is difficult and requires a fair amount of skill. When detected, the bug can simply move to a different position.
- In The Matrix, after refusing to cooperate during interrogation by Agents Smith, Brown and Jones, Neo has a bug planted inside his abdomen where the process jarringly played out like a rape; Smith placed the activated bug on the panicked Neo's belly as his cohorts held the latter on the table, leaving him helplessly struggled as it burrowed its way into his navel. It is later removed by Trinity and Switch.