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 placed on his abdomen, which burrows into his navel. It is later removed by Trinity and Switch.
- Ash in the Animatrix short film "A Detective Story" has a bug planted behind his eye during what he believed was an eye examination dream which was removed by Trinity when he found her.
- The scene where the bug enters Neo’s navel was intended as a rape metaphor, since Neo’s mouth is sealed shut and a phallic shaped object is forcefully penetrating his navel, with it representing an orifice.