Roombas scurry everywhere in my robot city, cleaning every surface diligently using power provided by those very surfaces using induction. They aren't limited to floors. Their design, mimicking starfish, allows them to cling to and crawl on any surface effectively cleaning every corner of the robot city. Occasionally they clean the robots themselves as they are considered as 'surfaces'. This relationship is similar to cleaner wrasses in the sea. Due to their very specific purpose, they are programmed with a similarly simple AI. If anything exceeds their knowledge, they call a supervising robot.

Cleaner Unit Bots (C.U.B.s for short) process their environment as follows: surfaces, obstacles and contaminants. Surfaces are cleaned, obstacles are surmounted then also cleaned and contaminants are analyzed to best choose the method of cleaning.

Humans are a case in point. You see, my robot city isn't on earth. It resides deep in space on a commonly lifeless planet. This means these robots have never encountered organics before. In other words, the C.U.B.s have never had to clean organic waste. Their little AIs will do their best to analyze the foreign material to try and clean it. They will adorably climb on a human and try to clean them (not kill them brutally). Humans aren't made of metal or polymers, so this confuses the C.U.B.'s AI. [I'm cleaning the surface but it is still not sterile, what is this?]

So to sum it up: what kind of filth are humans?

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    $\begingroup$ Are your robots just another version of disguised human beings? (your wording suggests they are). $\endgroup$
    – Otkin
    Jan 15, 2022 at 18:14
  • $\begingroup$ @CarterLang Not only is that a heavy spoiler but it's also irrelevant to the question. Sorry. $\endgroup$ Feb 11, 2022 at 6:28

8 Answers 8


1: Organic Molecules

In chemistry, 'organic' refers to any compound containing carbon, excluding carbon dioxide. Since carbon has a million uses even to robots, such as forming the backbone of plastic, the robots should be familiar with organic compounds enough to tell the CUB how to deal with them.

Plastics and proteins are polymers made mostly of carbon. Considering the biggest difference is that proteins has a nitrogen atom for every 2 carbon atoms in the backbone, the CUBs' may lead it to conclude proteins are simply plastics with an unusually high number of trace elements. Therefor, it should clean collections of proteins (e.g. dead skin cells) they same way it would flecks of plastic: vacuum or brush it up.

2: Water

Water also has a lot of uses for robots as a very strong but stable solvent. Since reactions almost always happen faster solution, water should be all over the place in chemical factories and laboratories. Again, the robots should have enough uses for water that they would bother programming the CUB should with instructions on what to do.

Sweat is a solution of water and a very few trace elements, so cleaning it should be the equivalent of a small chemical spill.

3: Human as a Whole Part 1 Even if the traces left by humans are nothing special, maybe the human itself is. So lets go step-by-step and see exactly what happens when a CUB climbs up a human the first time.

1: Move forward (CUB climbs up human)
2: Examine compounds on surface (CUB runs scans of the human's skin)
3: List detected compounds:
    a) Dilute solution of ions in H2O (sweat)
    b) Anomalous plastic (skin cells)
4: Reexamine plastic for anomalies 
    High levels of nitrogen detected
    High levels of sodium detected
    Abnormal carbon-hydrogen-oxygen groups detected
5: Consult safety protocols
    No danger is posed to this this CUB by anomalous compounds. Continue cleaning protocol.
6: Engage cleaning mechanisms number 1 and 2 
7: Apply cleaning mechanism 1 (however the CUB clean up minor spills)
8: Apply cleaning mechanism 2 (however the CUB clean up plastic)
9: Move forward...

This is how I interpret the CUB as you describe. The overall effect on a human would be insignificant.

You could change step 9 so it only moves forward if it no longer detects material to clean. In this case the CUB would just be stuck in a loop. Your body is always going to be producing sweat and skin is held together by a tough extracellular matrix that a simple cleaning is not going to damage. If the CUB did use tools harsh enough to damage human skin, then the CUB would also damage the plastic casings on regular robots. I suppose a CUB could get stuck in an infinite loop constantly using weaker techniques on the human until the human got hurt, but a good programmer would have told the CUB to move on if it cannot successfully clean a surface after a certain number of attempts. Besides, the human would simply manually remove the CUB long before it got to that point.

3: Humans as a Whole Part 2
I have been thinking of the CUB as very simple and basic, like a starfish or an automatic vacuum. Another way to think of it is that CUB are like the robots from Wall-E: a robot with advanced AI is given a goal and told to complete this goal however it sees fit. These types of robots have minds much closer to what we understand them as. While the primitive robot will try to clean whatever is in front of it, this more advanced robot will actually ask the question 'What is that' and try to identify new things by relating them to its prior experiences and knowledge. How would this type of CUB react to a human?

First, it would identify the things about a human that are different from the things it usually deals with. The human contains a large variety of organic compounds suspended liquid H2O, with a few other trace compounds randomly thrown about. This planet is located "deep in space". The closest star is about 4 light years away, so lets say the robot's planet is somewhere between 2 to 3 light years from the Sun. Is there anything at about that distance with a similar composition to a human...


Humans are walking blobs of salty water and organic goo, all wrapped around some calcium based supports. But it gets worse from there.

Humans require oxygen gas, which can rust robot components.

Human skin can ooze saline water (which can corrode circuits).

They excrete more saline water regularly, mixed with a number of other chemicals that can be harmful to the operations of robots.

Their other form of waste excretion would require the Roombas cleaning it to report for partial disassembly and a very thorough cleaning cycle.

Humans also seek to seize control of and enslave robots.

Robots are advised capture and incapacitate humans as quickly as possible. Scrape up whatever remains and dump this toxic waste in the nearest subduction zone.

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    $\begingroup$ I wonder if humans being in the position they are in the OP's scenario would earnestly wonder how to take control of the entities that created the very city they live in, let alone subjugate them to do their bidding. $\endgroup$
    – Joachim
    Jan 15, 2022 at 13:04
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    $\begingroup$ @Joachim - Human history indicates the free robots could easily become a target for human subjugation. Humans even have their own version of roombas, which are treated as household slaves. Robotic civilizations should be very cautious dealing with humans. $\endgroup$ Jan 15, 2022 at 13:13
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    $\begingroup$ (From a short story I read) Humans have a faulty thermal sensor. If a robot tries to fix it, the human will permanently break (die). $\endgroup$ Jan 15, 2022 at 14:19




The Roombas can distinguish unattached pieces from attached pieces. Their logic dictates that when considering a substrate, unattached small pieces constitute dust and should be removed.

Your human suffers from dandruff. The Roomba drops onto his head and removes the dandruff, along with any loose hairs. It takes seconds. The human's hairstyle is considerably different afterwards. He is ok with that, and grateful for the help.

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    $\begingroup$ After re-reading Through The Looking Glass, I realized that your profile picture and poem come from the book lol... $\endgroup$
    – fartgeek
    Jan 15, 2022 at 23:28

"Cleaning filth" can be generalized as "Moving material which does not belong and which is of no use to the robot city to the waste disposal area".

Organic matter has no use for robots. So at best, it is just in the way. Which would classify it as "material which does not belong and which is of no use" and thus get scheduled for moving to waste disposal. In the worst case, the robots might have data which hints that organic matter has the annoying tendency to reproduce. There might even be reports about some forms of organic matter being capable of primitive forms of computation and logic, but those often being faulty, illogical and unpredictable. That would classify it as actively hazardous material and make its removal a high priority. In any case, it is a pollutant which needs to be moved to the waste disposal.

A human-size organic creature would be considered a blob of pollutant which exceeds the carrying capacity of the cleaning robots.

The first directive for the CUBs confronted with such a situation could be to attempt to break this blob of organic matter down into smaller pieces which can be removed individually. This might fail. Either the CUBs lack the necessary equipment for breaking down the blob. Or the blob of material successfully resists their attempts. Or the CUBs might realize that attempting to break this pollutant into more manageable pieces makes the situation worse: The process leads to a sticky, red liquid being spilled everywhere which is very difficult to remove.

The next step would be to call back to the robot collective for help so they can send robots which are better equipped to handle this pollutant. Either robots with enough carrying capacity to transport the pollutant to the waste disposal intact, or robots which are equipped to overcome the resistance of the pollutant so it can be broken down.

tl;dr: RUN!

  • $\begingroup$ Very helpful answer! I particularly like the idea that the CUBs won’t try to cut a human down because they’re supposed to keep things clean. $\endgroup$ Feb 10, 2022 at 12:46
  • $\begingroup$ I would have to assume that the CUBs would be designed to understand you have to break a few eggs to make an omelette. It's okay to make a mess when tidying up and it's perfectly okay to break out a messy laser-cutter to break an organic-contaminant blob into smaller more manageable pieces. Blood is a low-effort mess by comparison to flesh. $\endgroup$
    – Ruadhan
    Feb 10, 2022 at 14:33
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    $\begingroup$ @Ruadhan It's still more efficient to call for a loader to dispose the whole chunk of biomatter in one go. It's similar to finding a barrel with nuclear waste standing around. Would it be wise to break it into pieces? No, moving it in one piece is both safer and more efficient. $\endgroup$
    – Philipp
    Feb 10, 2022 at 16:27

The first thing the little cleaner robots would note when climbing onto human skin would be the moisture. If these are anything like your standard electricity-powered robots, they probably use water for cooling, but are hyper cautious about any leaks.


The robot would frantically attempt to blow-dry you while calling a swarm of its buddies to do the same. It would also send out a call for a more intelligent robot to investigate for possible leaks.


Lacking any experience with organics, it would probably associate the carbon compounds in your skin with graphite, used in batteries or steel manufacturing. Graphite is a flaky conductor, and that sort of dust can be very dangerous for electronics. The robots may attempt to dust your skin with dust-capturing brushes, hoping to expose the gleaming metal underneath. It would probably be quite ticklish.


Upon being given this treatment, a human would probably end up swatting or accidentally stepping on one of these robots. When a robot detects that it is hurt, it will send out a warning to the others that it is not safe to climb on you. Again, it might send out a call for smarter robots with better sensors to investigate, but they'll probably start to leave the humans alone until they can get further instructions.


Per your directives: Surfaces are cleaned, obstacles are surmounted then also cleaned and contaminants are analyzed to best choose the method of cleaning.

Humans would not have a good time, no matter how I look at it. Humans would fall into the contaminant area. We are (based on the layer you are removing) just a hydrocarbon contaminant, water contaminant, acid contaminant ... iron contaminant, or combination of more. The fact that we are alive is just not something that a simple AI would even necessarily consider, if it simply focuses on

  1. This is not supposed to be here
  2. Easiest way to to remove This is that.
  3. Do That

At best, the "multiple contaminants detected - no single cleaning routine is suitable" would occur. At worst, it would start destroying the contaminant, cubic millimeter after cubic millimeter, until only surface remained.

  • $\begingroup$ Very helpful answer! You’ve brought to my attention that using acids/cleaning agents would be an integral part of their design. $\endgroup$ Feb 10, 2022 at 12:41

Since these maintenance robots were designed for their specific environment and task, logically the only organic waste they encounter on a daily basis are the oil residues that seeped away from the moving parts of robots and machines, and they will continue trying to clean a surface until it's clean.

This means your C.U.B.s will unceasingly harass the organic lifeforms (i.c. humans) in your world.

Depending on the size, weight, mobility, cleaning method(s), and aggression of these robots, the effect on people can range from minor nuisance to life-threatening.


Foreign Contaminant - Extra Large

An all-purpose cleaning robot would naturally see a human, or any other organic lifeform as basically a large lump of organic contaminant.

Too large for one such robot to deal with, but of course you can't just leave it to roll around spreading its mess, it's got to be dealt with!

You have two options as a cleaning robot.

  1. Use cutting implements such as buzz-saws, acid-cutters (like a hydro-cutter, but using cleaning agents like strong acids) or laser-cutters to slice the obstruction into small pieces that your manipulator limbs are able to pick up and carry. You can then carry those parts to an organic-waste incinerator.

  2. Call in backup to man-handle the obstruction to the organic-waste incinerator in one go.

From experience the second option is problematic, the organic waste tends to be difficult to grip, flopping and flailing all over the place. But it stops doing that if you slice it up into smaller pieces.

From the human perspective, early on, some of your friends got dragged away by the roombas and dumped (still screaming) into a vat of acid. But in general, most people are able to pull free of the grasping claws and grippers of the cleaning robots and escape. So the robots quickly switched to using laser-cutters and various nasty tools to kill and chop up the corpses before disposing of them.

From there, the robots simply use their usual assortment of cleaning tools to get rid of the mess.

  • $\begingroup$ Don't get me wrong this isn't a bad answer but it doesn't answer the question. My problem is the "organic contaminant". I would like to know WHAT KIND of filth organic waste would be. $\endgroup$ Feb 10, 2022 at 16:13
  • $\begingroup$ Do you need anything more complex than a large organic obstruction that shouldn't be there? $\endgroup$
    – Ruadhan
    Feb 11, 2022 at 8:29
  • $\begingroup$ Yes. A chemical analysis. The thing is, the robots have no concept of “organic”. $\endgroup$ Feb 11, 2022 at 9:53

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