I'm writing a speculative fiction story that includes superhumans. The focus is on individual characters and their daily lives, and I'm trying to maintain some consistency by not throwing all the laws of physics out the window. However, this creates some problems in the daily life of these individuals - where does their super-energy come from, given that they appear to eat a normal amount of food?

For example, a superhuman with super-strength is able to lift heavy objects. This is fine according to the laws of thermodynamics, as long as a proper amount of energy is used to perform it. To lift a 15,000kg semi 2 meters off the ground, my superhuman needs to contribute a minimum of 60 kcal. In a typical day, this character might perform an action like this 50 times, for an additional energy expenditure of 3,000 kcal - that's more than double the normal energy expenditure of a similar human. On intensive days, this energy cost might be closer to 20,000 kcal.

How can I justify this discrepancy between the energy my superhumans expend and the energy that they consume, assuming they eat a normal amount of normal food? Specifically, how could a superhuman obtain the 20,000 kcal expended in an intensive hero day without eating proportionally more?

Shoutout to the Sandbox for helping me develop this question!

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – James
    Nov 2, 2018 at 20:14
  • $\begingroup$ some excursions in the arctic require around 15Mcal a day. it's not unheard of $\endgroup$
    – tuskiomi
    Nov 14, 2018 at 15:43

15 Answers 15


Improved efficiency!

Lifted from https://physics.stackexchange.com/questions/46788/how-efficient-is-the-human-body

The MET (Metabolic Equivalent Task) readout on your gym equipment is your body doing 1Kcal/kg/h = 4184 J/kg/h and can be reasonably accurately measured by how much oxygen a test victim uses.

Sitting still is roughly 1 met and cycling at 100 Watts is around 5.5 Mets.

So taking a man of 75kg, cycling at 100Watts (100J/s) he is having to do 5.5 * 4184 * 75 / 3600s = 480Watts so an efficency of 20%

Remember though that the person is spending 80-100Watts just staying alive doing nothing - unlike your car. There is an interesting experimental fit to how much energy you need to just stay alive, calculated about 100 years ago, the Harris-Benedict equation

If your heroes are more efficient at energy conversion this can explain why they can get double or triple the energy from their food.


Fat heroes.

You can store a lot of energy in your body as fat and that is what your heroes do, with repeated trips to Wendys. I can vouch for that method. By virtue of their superhumanism, they metabolize that fat very rapidly to perform feats requiring great energy expenditures. Note: if their metabolism works normally mobilizing that much energy really fast would entail 3 other things.

1: Rapid respiration. They are burning that fat to CO2. They will need oxygen and lots of it. The might carry a little tank and portable mask, like Dennis Hopper in Blue Velvet. Or they might just breathe really fast. Or both.

2: Water production. CHO + O2 -> CO2 + H2O + energy. The water has to go somewhere. I propose they could sweat it out with supersweat glands.

3: Heat. Entropy takes its tax and that means a fraction of the energy goes to heat. These heroes will heat up when they do their stuff. Fortunately panting hard and sweating profusely will take care of most of that in the customary ways. Some heroes might augment onboard cooling abilities by putting ice in their pants before particularly heroic maneuvers.

Your obese, hungry, efficient heroes will be red faced, soaked with sweat and breathing hard when they do their super moves. They will look like Turkish power lifters. I say that is a fine change from the cool and composed thing you usually see!

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    $\begingroup$ I'm cracking up at the idea of an obese super hero that carries around an oxygen tank. They see trouble and start hyperventilating into their mask and do a bunch of superhuman feats. By the end they are at a healthy weight. $\endgroup$ Oct 30, 2018 at 21:20
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    $\begingroup$ @CaptainMan - then they hit Wendys like an atom bomb. $\endgroup$
    – Willk
    Oct 30, 2018 at 22:02
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    $\begingroup$ -1 Having an efficient metabolism does not make food contain more calories. An efficient metabolism is about the rate that calories can be delivered to the parts of your body that need it. $\endgroup$
    – Carl
    Oct 31, 2018 at 15:18
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    $\begingroup$ @Carl - A solar panel converts solar energy into electrical energy. Its efficiency is the % of available solar energy that turns into electrical energy. Delivery of energy happens after the panel does its thing. So too metabolism: our metabolism converts energy available in one form (reduced carbon) into energy we can use for activity. $\endgroup$
    – Willk
    Oct 31, 2018 at 16:04
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    $\begingroup$ @Carl no reason to make word games... "efficiency" can mean more than 1 thing depending on the contest. For example an efficient metabolism might not magically increase the calories in food but might be better at absorbing those calories, for example humans waste around 20% to 30% of the calories gained just to digest the food they eat, and most nutrients are lost during digestion.... $\endgroup$
    – user56803
    Nov 1, 2018 at 7:40

Your heroes are nuclear

Not exactly nuclear reactors, but if you're going to hand wave to the point where they are able to channel energy into superhuman acts, you can almost realistically justify that energy supply as coming directly from matter.

Ignoring small potatoes like potential chemical energy (our biological power source), go straight for the roughly 9x10^16 joules per kilogram (21.5 trillion kilocalories) that relativity suggests is in resting mass itself. If your heroes convert mass directly to energy, they have a basically unlimited source.

The only question at that point is why they need to continue eating, since a single meal would power endless exploits.

(Thanks goes to the Mass-energy equivalence Wikipedia page.)

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    $\begingroup$ They would still need to eat in order to get nutrients, even if they don't need the energy. $\endgroup$
    – Gene
    Oct 30, 2018 at 20:01
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    $\begingroup$ @Gene That's a fair point. $\endgroup$
    – Jedediah
    Oct 30, 2018 at 20:12
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    $\begingroup$ Perhaps they expend 90% of the resulting energy in containing the Matter/Energy Conversion process, so that they don't just explode? $\endgroup$ Oct 31, 2018 at 11:01
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    $\begingroup$ Nuclear energy only accounts for a small fraction of the energy from an atom's rest mass. A single nucleon has roughly 240 MeV in rest energy, given its mass, yet in typical matter, the nuclear binding energy per nucleon is around 6-9 MeV. To be fair, that's still a hell of a lot more than the molecular binding energy, which is what we use. The only way to utilize all 9 * 10^16 J/kg, as you suggested, is to annihilate matter with antimatter. $\endgroup$ Oct 31, 2018 at 16:45
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    $\begingroup$ sounds like the Cherenkov-Kirby Reaction from the spinerette universe. Nano scale biological fusion reactors that power supers $\endgroup$
    – John
    Dec 8, 2020 at 5:53

The classic canonical energy source for Superman was "our yellow sun" and though this seems ludicrous in some senses today, you could crib from this in some interesting variants:

1) Photosynthesis: your supers actually generate chemical energy and store it hyper-efficiently in special cellular ATP bins, which standard humans don't have, not to mention our not being able to directly convert light into chemical energy.

2) Magneto-electrical: your supers have radically different cellular biochemistry as well as cellular physiology from standard humans, with naturally filtered ferromagnetic particles forming an essential part of their super metabolisms; as a result they generate electrical energy as they move through the Earth's magnetic field via induction, and the carbon nanotubes woven into their cellular mytochondria focus and transport this energy to per-cell electrical storage stacks - this energy is stored to be released in high bursts like a natural capacitor, and is used to catalyze their already hyper-efficient metabolisms at the cellular level. Some supers can store and channel this energy at a system level also - hence Ororo / Storm style lightning throwers.

3) Cosmology-physics 01: your supers basic matter are composed of particles/strings which are unusually vibrationally aligned in several of the more obscure of our 11 dimensions such that they gain energy from moving across certain by us unobserved symmetry-breaks (sort of like getting and releasing potential energy from climbing and jumping off boulders) but they must pay careful attention to direction and orientation of these breaks as they move through them, as they could make a mistake and subtract energy if incautious.

4) Cosmology-physics 02: your supers have a metabolic constituent which is en masse quantum entangled with regions of higher-energy particles which occur inside stars (hence the Superman - yellow sun misunderstanding of the past) and which provide them unceasing energy throughout their lives as long as the star to which they are personally aligned continues to perform as typical for a main sequence star. In fact, if they don't find an outlet for all this extra energy, they will spontaneously combust - hence both the 'drive' they all seem to have for performing superfeats all the darn time and the rash of unexplained spontaneous combustion deaths in the 1970's - lazy, stoned supers not getting they supergame on.

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    $\begingroup$ The photosynthesis thing was done in "Nights of Sidonia" in order to allow humans to survive in space with limited food resources. $\endgroup$
    – user4574
    Oct 31, 2018 at 15:08
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    $\begingroup$ @user4574 I believe it was Knights of Sidonia, btw. $\endgroup$
    – TylerH
    Oct 31, 2018 at 19:14

Super Dense Foods

In another world building question we dealt with magical bread that contained 2,000 Kcals per bite. The Most accepted answers states this bread is:

nearly as dense as granite

However your super human has super human strength and super human bite pressure. He can chew this bad boy up like a cold cereal!

Considering you need 20,000 Kcals you only need 10cm^3 of the stuff for a whole day of super human saving!

  • $\begingroup$ This is the approach that I would use. Combined with the "Improved Efficiency", I think you can build a very solid argument $\endgroup$
    – Cenlan
    Nov 1, 2018 at 14:26

Your superheroes may rely on Ch'i / Qi / Ki or any variants of the same principle (like "the Force" in star wars). It could explain the difference in energy. The superheroes are able to harvest energy from life itself. Qi by itself is not proven by science (from link above):

Qi is a pseudoscientific, unverified concept, which has never been directly observed, and is unrelated to the concept of energy used in science (vital energy is itself an abandoned scientific notion).

However, eastern spiritual streams and religions strongly believe in Qi. For instance an introduction can be found on this site.

Qi is the Chinese term for life energy, or life spirit, a vital force that flows through all living things. It is an essential part of acupuncture, qigong, reiki, and the martial arts of the East, among other things. There is no mystery to it.

Dragon ball series used this to overcome the same problem:

Because there are physical limits to the strength of the body itself, it is necessary to increase one's ki to overcome this barrier and become stronger.

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    $\begingroup$ OP says "not throwing all the laws of physics out the window", Qi throws all the laws of physics out the window. $\endgroup$
    – crobar
    Nov 1, 2018 at 9:34
  • $\begingroup$ As someone who has studied a bit of Chinese, this is funny to me, as while yes, Qi is the name of mystical and magical power, it is also the same exact name for gas (as in the state of matter) and just plain old average energy - 气 $\endgroup$ Nov 1, 2018 at 16:19

Alternate energy sources: Obviously, for a world to have superheroes must needs break at least some of our assumed laws of physics. I think the cleanest resolution would be for the distinguishing factor of superhumans to be the access to some other form of energy not normally accounted for.

One of my favorite Asamov stories, The Gods Themselves includes the concept of exploiting access to a parallel dimension, in which physics works subtly differently than in ours, to derive massive amounts of energy.

Imagine some quirk of quantum mechanics which allows certain conscious beings to tap into some other dimension at an unconscious, subatomic level. They would be channeling what amounts to a difference potential in atomic forces. In fact, if you posit infinite parallel worlds, the variations in super powers could be due to the variations in universal laws.

That way, most of the physics in your world work the same as what we normally assume. And, there wouldn't necessarily be any obvious difference in biology (which has often been bothersome to me in certain Superhero world-concepts; evolution doesn't work like that dammit).


They can freely manipulate fields

These superhumans have developed an organ controlled by their brain that lets them manipulate different fields (electromagnetic, gravitational, higgs?, etc.) Each individual can manipulate each field differently and so their powers manifest differently. The food they eat is used for regular body functions including this new organ, so they may eat an athlete's worth of food as a result of using their powers. The power itself is a result of which field(s) they can manipulate and how they're manipulated, so their skills also require a bit of brain power and practice to get right.

Since there may be a multitude of different kinds of powers, here's a quick list of how some powers might be explained in this scenario:

  • super strength: anti gravity (weaken gravitational fields) against external objects + EM to strengthen skeletal system
  • flight: anti gravity against self
  • lightning/energy blasts: manipulate EM fields to produce charges or focus photons
  • invisibility: (EM) bend photons around an object
  • teleportation: manipulate gravitational fields to bend space between two distant locations (free time travel?)
  • regeneration: this one's tricky. Cells could be forced to replicate quickly via chemical signals (no field changes required) but this would require a lot of energy (and concentration?). Another option might be to use gravitational fields to locally reverse time on parts of the body, or the body as a whole. Unintended side effect: the individual forgets what happened before the incident after full-body recovery.
  • super speed: another tricky one. Perhaps the individual makes him or herself lighter and/or manipulates spacetime so that everything around them slows down.

Overall, using this method you can minimize energy expenditures while explaining a wide variety of super powers.

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    $\begingroup$ How would said organ weaken or strengthen said fields? As far as we know, nothing in real physics allow for weakening of gravitational fields, for instance. Gravity is universal. The only way to weaken at least one body’s gravity on another body entirely is to increase the distance between them, but it has to be an unfathomable immense change of distance, as gravity is weakened less by distance than any other force except electrostatics, which has the same inverse-square law dropoff. $\endgroup$ Feb 6, 2023 at 22:27

First of all, you won't get a science-based answer simply because things don't work that way in the real world. "Calories in = calories out" is one way to look at it; conservation of mass and energy is another.

You're effectively looking for a plausible-sounding pseudo-science explanation, at most, regardless of whether you want to admit it. That said, it is entirely up to you to decide how far you drift from respectable scientific ideas.

1. Explain only what you need. Unless the mechanism behind a superpower is necessary to develop plot or character, don't discuss it. This is a good general rule in writing.

2. Convert mass to energy. A minuscule amount of mass creates an enormous amount of energy---from a human perspective. If your superhumans are somehow doing this, they are capable of tremendous feats with little "food" consumption.

3. Sci-fi with clear knowledge. You can make things sound science-based without actually being scientific at all. E.g., you start with "Several new metabolic processes have been identified in superhumans which allow..." and then explain briefly how they can extract more usable calories from food, engage in some sort of photosynthesis, etc.

(I remember some science speculation about ATP with extra phosphoryl groups, for instance, but that's more like a bigger battery than a bigger generator. Plus, it probably didn't evolve in any known creature for a reason.)

4. Sci-fi with limited knowledge. Contemporary science can detect fields, energy waves, etc around these superhumans, but it cannot explain how their abilities function. There are always unexplained phenomena at the edge of science, so this isn't anything new. You can make the phenomena seem more science-based by mentioning any measurable effects, which scientists would observe and investigate.

5. Quasi-magical. You said you didn't want this, so I mention it only to complete the spectrum. Sci-fi encroaches here often anyway. Most people have zero understanding of quantum theory and string theory. You could make up almost anything, and most readers would roll with it. This may irritate physicists and pretentious intellectuals because it flies in the face of established science, but a non-starving Superman flies in the face of established science to begin with.


Higher efficiency: Human muscles only have ~30% efficiency. If your superhumans have almost 100% efficiency they could do three times the work without needing more food.

Lower resting metabolism: Humans need ~1500kcal per day just to stay warm and alive. Your superhumans could have a lower body temperature, better insulation, hibernate during sleep (and sleep a lot) or anything else to reduce this requirement drastically.

A normal human male burns about ~2500kcal when running a marathon. With the above modifications your superhumans could run more than two marathons without needing extra food (compared to normal, sedentary humans) on that day.


The figures you put in your question are not so impressive...

Consider a sumo wrestler:

The ideal weight for a sumo wrestler is anything from 400 to 600 pounds. This means that it takes not only strength and flexibility to be a sumo—it also takes the right diet. Eating is an essential part of their training.

A typical sumo wrestler eats a daily diet of 20,000 calories, which is pretty astounding when you consider that the recommended daily intake for a healthy, active male is 2,500. They eat 10 times what a normal male eats and all of it’s done in two massive 10,000-calorie meals.

Your superhero is basically a slim sumo wrestler in Lycra pants...

Here is a typical sumo wrestler daily eating schedule:

Skip breakfast

A sumo wrestler’s day starts at four or five o’clock in the morning with training and exercise. Surprisingly, breakfast is not served. Skipping breakfast and working out instead slows down the wrestler’s metabolism, so they usually don’t eat until around 11am. It also gets them hungry enough for that 10,000-calorie lunch.

Bulk load

The main dish that sumo wrestlers eat is a stew called chankonabe (ちゃんこ鍋). It sounds a little like ‘chunk nabe,’ which is somehow oddly appropriate. This is a stew filled with fish, vegetables, meat and tofu. Nabe (鍋) is a traditional Japanese stew, but chankonabe is the supersized version, stuffed full of extra everything for the sole purpose of providing calories. To complement their mighty meal, sumo wrestlers eat around 5–10 bowls of rice and copious amounts of beer, required for empty calories. A healthy rikishi (力士, sumo wrestler) may down as many as 6 pints during the midday meal.

Take a siesta

After lunch, there’s one more essential bit of training—the nap. How could you not pass out after a meal like that? Sumo wrestlers take a siesta for as long as 4 hours after lunch, in order to slow down their metabolism and add everything they just ate to their girth.

Dinner and lights out

At the end of the day, sumo wrestlers eat another massive meal and call it a night. While they sleep, the day’s protein and calories work their magic and they wake up in the early morning ready to smash their bodies against each other.

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    $\begingroup$ This doesn't seem to actually answer the question. The numbers I gave are just an example - a superpower like flight would require more, and if a superhuman with the ability to carry a building is going to obey the laws of thermodynamics then they'll need more than even what sumo wrestlers consume. $\endgroup$
    – Dubukay
    Oct 30, 2018 at 16:46
  • $\begingroup$ It's your world, I can only answer based on the info you provide... $\endgroup$
    – L.Dutch
    Oct 30, 2018 at 16:49
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    $\begingroup$ Regardless, I did request that they consume "a normal amount of food". I don't think that the amount of food a sumo wrestler consumes is considered "normal". It might be normal to them, but not to an average human. $\endgroup$
    – Dubukay
    Oct 30, 2018 at 17:04
  • $\begingroup$ @Dubukay "a superpower like flight would require more" - I think if you're trying to justify believable superhumans then flight is going to give you a lot more problems than calorie consumption... $\endgroup$ Nov 1, 2018 at 16:34

Organic Cold Fusion

Cells or an organ takes water and can detect if it is heavy water. If it is it breaks it down to deuterium and oxygen. It then takes the deuterium and with some hand waving fuses it together to make helium. This in turn releases massive amounts of energy that can power the super hero.

From the outside all you notice is that the hero drinks extra water and releases a bit of helium as a waste product.


I think the main problem is the energy storage. Your heroes can eat 20kCal by eating food (10 big macs with extra fries) all day long and drinking (+10 glasses of vodka and enough nuts to go with it) all night long, which will fit nicely to any story. Also they might recover their energy not in a single day but could take multiple days.

Now energy problem: you need superhuman metabolism to become superhuman. Do not think this as a higher functioning human metabolism. This one is different. Instead of ATP, sugars and fat, superheroes store their energy in a much more energy dense molecule which requires same amount of oxygen as sugars to burn but generates much more energy. Thus they do not store energy in sugar or fat but this ready-to-burn, extremely high calorie molecule which is also stored in blood for quick access.


The answer is simple ..

dark matter

Says it all.

Note that the acts performed by "super-beings" are ridiculously outside of conventional physics.

Remember "the Six million dollar man" .. ? Sure, his arm was, let's say, some hyper material with incredibly strong motors. But when me picked up a car ... it would have just crushed the other parts of his body. In a similar way Superman simply could not do the things he does, even if his body per se, is astoundingly strong / powerful in a conventional sense.

Super-beings go around conventional matter-energy physics. It's obvious this involves dark matter / dark energy (which after all, bends galaxies .. !!!!! .. in a totally non-Newtonian manner which is completely mysterious to us).

Your super beings need conventional food only for their conventional metabolism and physics Newtonian spreadsheet.

The rest .. it's dark matter / dark energy. The same force system - which we currently do not know or understand - which bends galaxies against the conventional gravity of a whole galaxy - holy crap!

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    $\begingroup$ You might be a little confused about Dark Matter. Since we don't know what it (or Dark Energy) is, one can not say that it isn't just simply matter that absorbs light. If, as the OP said, one does not want to throw all physics out the window, one should not ascribe convenient superhero properties to Dark Matter, since we know there are things it does not do. $\endgroup$
    – JWT
    Nov 1, 2018 at 15:27
  • $\begingroup$ hi @jwt ! We know exactly what dark matter / dark energy do, quantitatively. They are a completely unknown, conveniently not understood force so powerful they can counteract the force of gravity of a galaxy. (!) You can read about it on any wikipedia site. Thus, the perfect placeholder in a story which attempts to explain the strange powers of Supers. Handwaving without handwaving :) (By all means, the OP may prefer the idea of "counting calories". But, as I try to explan, that simply doesn't explain the physical impossibility (energy delivery, lack of deformation, etc) of supers!) $\endgroup$
    – Fattie
    Nov 1, 2018 at 17:21

A simple way to make up the calories is if your characters drink two liters of canola oil per day. A liter of canola oil has over 8,000 calories. Combine that with more efficient digestion and usage of calories, and maybe they could cut that down to just a liter a day.


I often go with the "Superman" supplement route as described, but essentially diversify my range of energy sources. A lot of my superhumans exhibit some sort of... vampirism... that fuels their abilities. For example, my character with a Superman set of powers has them only while he holds an electrical charge. If he's low on power, he either has to conserve his ability use OR hope that one big burst of power can save the day OR find a sorce electrical energy fast. Either way, without holding any charge, he's as human as the innocent bystandards (I first came up with the character when Twilight was big... I billed the concept as a "Sparking Vampire" to play on the complaint of the "Sparkling Vampires".)

Other characters powers will eat at them unless they can find a source of fuel. For example a villain with telepathic and telekinetic powers would burn up his body if he doesn't feed off of other psychic energies to survive... which is fatal to his victims... thus, he can't consume the energy needed to do what he does by eating enough calories and needs to feed.

Other times, the lack of proper fuel is unrecoverable and part of the character's journey... it will be fatal and what they do with their abilities for their shortened life will be important. While this isn't the exact reason for it, I often attribute this to the reason why Bizzaro is Superman's clone (that is, the person who clones Superman did so believing that Superman was human and not an alien, so the result degrades because of the differences in physology between the two and the clone being unable to synthesize the protiens required for superman to do what he does). This was also discussed in the original Jurrassic Park film when they talked about the Lysine Contingency where the dinosaurs were genetically engineered to not produce the amino acid lysine and needed to consume it to prevent "slipping into a coma and dying" as Samuel L. Jackson explains it in what has to be his least badass attempt to kill something. Suffice to say, it was supplemented in the dinosaur's diet by humans (and if something went wrong, they would die out in a few days of denial of the supplement). Although this is highly unrealisitic, it's the general idea in that the extra energy requirements are features not bugs, when the superhuman is manufactured by someone seeking to control him/her (The reason the Jurassic Park example is bad science is because NO VERTIBRATE can produce lysine and have to have it supplied through diets. The sequel points addresses this when they point out the herbivores eat plants which do create lysine and the carnivors eat the herbavors, and get it that way... which in universe does work as the first film did point out that Hammond's attempts at control over animals no one has seen alive is woefully inadequate to the point of negligence.


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