On numerous occasions, we see the Agents moving in and out of people who're still hardwired to the Matrix. They appear to see what they see (as evidenced by the Vagrant in the subway who sees the team jacking out) and can move in and out of them with no apparent difficulty.

They physically manipulate Neo by changing his self-image to remove his mouth and then implant a bug in him.

What did the bug do and why was it needed if the Agents can already see what bluepills can see?

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  • 14
    Other than being super creepy, obviously.
    – Valorum
    Oct 23, 2014 at 22:38
  • 3
    Here's a thought: the Agents knew Morpheus was trying to unplug Neo so they are trying to find Morpheus through Neo. If Morpheus picks up Neo to unplug him but blindfolds Neo (and no other bluepill sees Morpheus or Neo) then the Agents can't track Neo's location. The tracking bug removes the limitation that the Agents require bluepills to see something. It's a failsafe.
    – Null
    Oct 23, 2014 at 22:53
  • Except that they don't blindfold him. They tell him exactly where they'll be, then wait a while before taking him there.
    – Valorum
    Oct 23, 2014 at 23:01
  • 1
    The Agents don't know Morpheus wasn't planning on blindfolding him. Why risk failing to capture "the most dangerous man alive" for lack of a bug?
    – Null
    Oct 23, 2014 at 23:12
  • 3
    I like the identifier theories. "There are only two hard things in Computer Science: cache invalidation and naming things." -- Phil Karlton Even Artificial Intelligence hasn't thought up a way to uniquely and efficiently identify things in a massed sea of objects.
    – Dacio
    Oct 24, 2014 at 20:06

2 Answers 2


Under normal circumstances Agents cannot distinguish individual bluepills from each other, so the bug is used to mark a specific bluepill and track his location.

The Machines' bug is analogous to the Zion operatives' red pill. Recall Morpheus' explanation of how the red pill works:

The pill you took is part of a trace program. It's designed to disrupt your input/output carrier signal so we can pinpoint your location.

transcript for The Matrix

The red pill is designed to help determine a specific bluepill's location in the real world, while a Machine bug is designed to help determine a specific bluepill's location in the Matrix (and possibly the real world as well). With billions of bluepills "just living out their lives" in the Matrix, it is impossible for Agents to find a specific bluepill among all the other bluepills in the Matrix, and it is impossible for Zion operatives to find a specific (ex-)bluepill among all the other bluepills in their Real World pods. To borrow a quote from Cypher:

But there's way too much information to decode the Matrix. You get used to it. I...I don't even see the code. All I see is blonde, brunette, red-head.

transcript for The Matrix

The red pill disrupts a bluepill's input/output carrier signal to "mark" him, and the bug similarly "marks" or "highlights" a bluepill to distinguish him from all the other bluepills. In a sea of indistinguishable blondes, brunettes, and red-heads the red pill or bug makes an individual distinguishable, as if that person was the only one with green hair.

Without the bug

Agents can "see" what any bluepill sees but since there are billions of bluepills it is impossible to look in real time at what all of them are seeing to pinpoint the location of Zion operatives anywhere in the Matrix. This exhaustive search can only be narrowed down if a bluepill sees something unusual (e.g. an operative breaking the rules of the Matrix) and/or if Agents know the rough location of the operatives (such as when they are in a chase, in which case they can check only what is seen by the relatively few bluepills in that area). In the case of the vagrant in the subway, the Agents had been chasing Neo and Trinity so they knew roughly where they were; they undoubtedly checked what the vagrant saw (especially since he was in view of a phone the operatives could use to jack out) and Agent Smith possessed him when he recognized Neo and Trinity.

With the bug

There are two known uses of the bug. In Neo's case the Agents were attempting to locate Morpheus, so they needed to know Neo's location when he met with Morpheus. Since the Agents can't distinguish Neo from all the other bluepills and Morpheus could meet Neo anywhere in the Matrix, they need to mark Neo with the bug. This also explains why Agents don't try to possess Neo after the bug is removed but before he actually takes the red pill -- once the bug is removed from Neo they can't tell which bluepill is Neo out of all the other bluepills in the Matrix. They don't know where he is, and so they cannot possess him.

The other bug appearance is in A Detective's Story. Agents placed an eye bug in the detective Ash in order to obtain Trinity's location when Ash met her on a train. The Agents had "hired" Ash to locate Trinity so they were obviously monitoring him. But they can't distinguish Ash from other bluepills under normal circumstances, so they put a bug in his eye to track the location of Ash specifically. When Trinity removes the eye bug the Agents can no longer track Ash, but they know the location of the bug was when it was removed and they know only a Zion operative like Trinity could remove it -- that's when Agents start possessing other bluepills on the train.

If Agents could simply possess any particular bluepill without a bug it would have been trivial for them to possess Neo as he met with Morpheus or Ash as he met with Trinity. For that matter, they could stop Zion operatives from unplugging any bluepill by possessing that bluepill just before he took the red pill. The bug allows the Agents to mark particular bluepills so they know where they are and which bluepill to possess.


I don't think it is ever specifically addressed, but at least three reasonable theories present themselves, based on the bug's appearance/use and the behaviors/limitations of the Agents throughout the trilogy:

A more sophisticated surveillance suite

We know the Agents can sense things happening through the eyes of the bluepills by the way they show up so quickly where they're needed, but we don't know the limits of that ability. It's entirely possible that they can only draw basic information through this method, and need something more to get true surveillance on a subject.

If, for example, they can passively scan for information like "encounters with unregistered users" (i.e. redpills), the bug might provide more sophisticated scanning and data collection regarding visual images, event logs, field analysis, etc. Alternatively, it could provide information from more senses (e.g. sound in addition to visuals) or higher resolution/quality/detail than normal.

Not just a bug, a weapon

For a surveillance tool, that thing sure comes off as aggressive... We know that Agents can't just arbitrarily "eject" or kill people in the Matrix, they have to manifest nearby and manually kill them. The bug could be a way for them to exert more direct control on a suspect, hurting or killing them in addition to gathering information on their location or activities, without having to physically show up and start shooting.

Software that follows you into the real world

This was always my assumption. We see from Agent Smith's "assimilation" of Bane that code can be uploaded into a human brain and remain there even after the user unplugs. Seeing as how the Agents knew of Morpheus's interest in Neo by then, it's possible that the bug was a subroutine that would have remained in Neo's mind when they pulled him out, uploading information about his offline activities whenever he jacked back in.

  • 1
    I like the third suggestion. We know from "Detective Story" that they have an eye bug as well. I'm not sure what extra useful info you'd gather from a stomach bug.
    – Valorum
    Oct 23, 2014 at 23:14
  • I like the third suggestion, too. The only thing I don't like about it is that Smith's assimilation of Bane didn't occur until the sequels, which meant that this question from the first movie would have remained unexplained for years until the sequels came out.
    – Null
    Oct 24, 2014 at 4:59
  • 6
    @Richard Stomach bugs could analyze the pills. Oct 24, 2014 at 8:25
  • @ceesTimmerman - I like that. Clever.
    – Valorum
    Oct 24, 2014 at 9:39

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