Editing 1839: Doctor Visit

{{comic
| number    = 1839
| date      = May 19, 2017
| title     = Doctor Visit
| image     = doctor_visit.png
| titletext = According to these blood tests, you're like 30% cereal.
}}

==Explanation==
[[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 {{w|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% {{w|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 {{w|cereal}}, the edible part of a grain, making the comparison apt.

All things taken into consideration, {{tvtropes|BackAlleyDoctor|we don't actually have any confirmation that Ponytail is a real doctor}}. As Randall has stated before, [[699: Trimester|anybody can just buy a lab coat]]. Although Ponytail's answer in the final panel lacks [[1644: Stargazing|the usual "I have no idea" or equivalent non-answer]], it's still somewhat possible she's a real doctor having an existential episode.

Another explanation, is that Ponytail is possessed by an alien intelligence, which would explain her lack of understanding of human physiology (see https://www.explainxkcd.com/wiki/index.php/1541:_Voice).

==Transcript==
:[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.

==Trivia==
Later Doctor Ponytail offers these thoughts again as an internal monologue in [[2057: Internal Monologues]].

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Biology]]
[[Category:Doctor Ponytail]]
[[Category:Medicine]]