Explain xkcd: It's 'cause you're dumb.
Cueball is visiting his doctor Ponytail, apparently for a general medical checkup.
While there is nothing wrong with him medically, the doctor wonders why he has continued to work for many years despite his body parts' individual fragility. Compared to man-made structures - like the USB cables mentioned by Ponytail, which quickly begin to fray - it's surprising that the body can survive for so long while sustaining so much wear and tear. Actually the body gets stronger and more fit the more it is used (an example of antifragility), in contrast to USB cables, which tend to wear out with use.
Ponytail specifically mentions his eyes which are so fragile and exposed. Yet most people go through a whole life with both eyes intact, although the vision itself may be impaired. The human reflexes and the shape of the skull around the eyes has a lot to do with the fact that it is possible to protect such fragile structures for a lifetime.
Ponytail also remarks that the body is composed of high pressure fluids (particularly blood, intracellular and extracellular fluids) and intricate parts (like the nervous system and the heart). If the fluids stopped flowing or the intricate parts stopped working, the entire body would fail, killing Cueball.
It should be noted that the human body is constantly replacing dead/injured cells and proteins. In a young human body, everything in the body is continually refurbished, and nothing is able to become old enough to deteriorate unintentionally; this requires a constant supply of energy and nutrients to keep this process going. As the body ages, these self-repair mechanisms eventually slow and can no longer keep up with the required repairs; this manifests as the various symptoms of old age (wrinkled skin, graying and balding hair, worsening eyesight and hearing, etc.) and eventual death.
USB cables are built to withstand far more wear and tear than the human body. But while this makes them tougher than blood vessels on the outset, they inevitably fray and fail faster than blood vessels because they lack the self-repair mechanisms of organic material.
The doctor's final remark is that Cueball is mainly made from dissolved bread, which is true from the perspective that the food (bread) he eats is digested in his alimentary system, absorbed into his bloodstream and used as nutrients for growth and repair. Paleontologists use a method called isotopic analysis to determine the diets of ancient people from elements preserved in teeth and bones. Ponytail could have ordered a similar test on Cueball.
This is taken further in the title text, where she states that the blood tests reveal he is 30% breakfast cereal. This likely comes from the widely-cited but not entirely accurate factoid that the human body is 70% water. The other 30% would then be flesh and other organic matter, or the dissolved bread the doctor described. Breakfast cereal and bread are both products of cereal, the edible part of a grain, making the comparison apt.
All things taken into consideration, we don't actually have any confirmation that Ponytail is a real doctor. As Randall has stated before, anybody can just buy a lab coat. Although Ponytail's answer in the final panel lacks the usual "I have no idea" or equivalent non-answer, it's still somewhat possible she's a real doctor having an existential episode.
- [Cueball is seated on an medical examination table while Ponytail stands dressed in a doctor's coat holding a file in her right hand.]
- Cueball: Everything look good?
- Ponytail: I don't get how your body has been moving around for years and still works at all. My USB cables fray after like a month.
- Ponytail: Your heart has been pumping for decades without pausing for even a few minutes.
- Ponytail: And your eyes! They're so fragile and exposed!
- [Zoom in on Cueball gazing at his palms.]
- Ponytail (off-panel): You're full of all these high-pressure fluids and intricate parts that could kill you in seconds if they stopped working!
- [Zoom out again to the entire scene.]
- Cueball: ...can you just tell me whether I'm healthy?
- Ponytail: Yeah, you're fine.
- Ponytail: Which is weird, given that your body is basically made from dissolved bread.
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This comic seems relatively simpler to explain. Nialpxe (talk) 06:38, 19 May 2017 (UTC)
I don't have the desire to edit this at the moment. However, it should be mentioned that when studied and considered critically the human body is actually quite resilient. We are merely used to thinking of "strong" and "tough" as properties of metal, which to someone unfamiliar with the materials which make up Human organs may associate them as being squishy and therefore weak. The human eye itself is perhaps vulnerable as it is a delicate instrument but it is not weak. Moreover the human body is self-renewing and of a far higher quality of function and design than any technology we have created. --Lackadaisical (talk) 13:16, 19 May 2017 (UTC)
- Anyone who thinks metals are strong and tough should talk with dentists about length of warranty on dental crowns. But yes, the main advantage of human body is the self-repair capability. (Note that I have cables which works for years, but maybe I don't manipulate them so often.) -- Hkmaly (talk) 22:41, 19 May 2017 (UTC)
- 30% Cereal
Am I the only one who doesn't get that one?
188.8.131.52 10:08, 19 May 2017 (UTC)
I'm pretty sure the 30% cereal is a reference that the human body is made of 70% of water. 184.108.40.206 10:46, 19 May 2017 (UTC)
But blood has around 90% of water. Can a blood test tell how much water Cueball has ? 220.127.116.11 (talk) (please sign your comments with ~~~~)
This possibly has to do with the fact that numerous things produced by the body, such as hair, are partly produced from consumed high fructose corn syrup which is found in cereal and countless other foods as a sweetener.  18.104.22.168 12:37, 19 May 2017 (UTC)
- I always thought that HFCS tasted like hair. Now I know what it's made of! *spits out beverage* (Just kidding. They don't use HFCS in my country.) Nialpxe (talk) 12:48, 19 May 2017 (UTC)
It seems that Randall recently read the book "Antifragile" by N. Taleb :) 22.214.171.124 (talk) (please sign your comments with ~~~~)
I think it refers to that 70% of a human is water, I guess. 126.96.36.199 13:39, 19 May 2017 (UTC)
That kinda reminds me of those Code quality strips. The overall tone in all of those is "How did you manage to get it working?!" 188.8.131.52 14:36, 19 May 2017 (UTC)
I was reading the 30% cereal comment as a play on the 'you are what you eat' idea. Three meals per day plus some snacks would make breakfast (cereal) about 30% of the diet. 184.108.40.206 15:28, 19 May 2017 (UTC)
I think this strip makes a lot more sense if you replace Ponytail with Zoidburg. 220.127.116.11 19:44, 19 May 2017 (UTC)
Am I the only one that thought "bread" referred to carbohydrates, and everything they break down into? 18.104.22.168 04:22, 20 May 2017 (UTC)
Anyone else think this has to do with Trump's latest stupid comment about the body having finite energy like a battery and it being a bad idea to exercise? 22.214.171.124 05:33, 22 May 2017 (UTC)
I thought that too, about the "finite amount of energy" comment from djt, but Randall mostly seems to avoid political commentary. PocketBrain (talk) 12:39, 22 May 2017 (UTC)
Am I the only one that thinks that Ponytail might not be human - Referencing "my USB cables" bring part of herself that she needs to replace regularly from carrying out normal human activities? This would also explain her surprise at how the human body functions 126.96.36.199 16:25, 22 May 2017 (UTC)
- You might be - in all honesty, I frequently think these same kinds of thoughts myself, and this may just be Randall's way of presenting them to us. I don't believe this has anything to do with aliens or possession. Just my $0.02 --Ianrbibtitlht (talk) 22:13, 9 June 2017 (UTC)
You know what we need? Biological self healing USB cables. Problem solved. 14:05, 23 May 2017 (UTC)
You would have to feed them and clean up their excrement - that's trading one problem for two.
On second thought, they could be plant based. -- 188.8.131.52 (talk) (please sign your comments with ~~~~)
- They should definitely be plant based - we don't want them to move on their own. Still, keeping them on sun often enough and watering them would be easy to forget. Also, plants are not really good at conductivity ... but we could have biological optical cables. Or have normal cables and only use plant-based isolation on them - that should still make them last considerably longer. -- Hkmaly (talk) 03:14, 27 May 2017 (UTC)