In ancient Japan, your emotions were never truly yours – they belonged to someone else. And modern science is starting to prove them right.

The night air is thick with moisture and lamp smoke, and on the walls the tangled shadows of a dozen people who have no intention of sleeping tonight twist and fidget. It is a kōshin (庚申) night – the fifty-seventh in the sixty-day cycle of the calendar, and everyone here knows that on this one night they must not close their eyes. Not because of thieves, not because of fire, not because of earthquakes. Because of what lives inside them. In the head, heart and belly of every person in this room dwell three creatures called sanshi (三尸). All day long they are imprisoned. But when a person falls asleep, they escape the body, fly toward heaven and file their report. They inform the celestial lord Tentei of every lie, every moment of laziness, every impure thought. And Tentei shortens that person’s life in return. The only defence: don’t let them out. Sit, talk, drink sake, play games, recite poetry – and under no circumstances fall asleep.

If someone told this story to a psychiatrist in the twenty-first century, the psychiatrist would nod with polite understanding and jot something in a notebook. But if that same psychiatrist read the latest studies from Caltech, McMaster University and the University of Cork, an eyebrow would rise. Because modern neuroscience has discovered something that sounds disturbingly similar: living organisms inside the human body genuinely influence emotions, mood and behaviour. Only we don’t call them mushi (虫 – worms) – we call them gut microbiota. And they don’t fly to heaven to file reports – they send chemical signals to the brain via the vagus nerve. The effects can be equally dramatic: a gut bacteria transplant from an anxious mouse into a bold one changes the bold mouse’s behaviour. Bacteria from the intestines of people suffering from depression, introduced into laboratory mice, produce depressive behaviour in those mice. Something that lives inside us – something that is not us – controls how we feel.

The Japanese had a single word for this: mushi (虫). Worms. Creatures within. For a thousand years, Japanese folk medicine, folklore and everyday idioms treated emotions not as a person’s property but as the activity of something that dwells inside them and has a will of its own. Anger was not your anger – the worm in your belly refused to calm down. A child’s irritability was not the child’s fault – a kan no mushi (疳の虫) had nested in its spine. A premonition of coming misfortune was not a sixth sense – it was mushi no shirase (虫の知らせ), a message from a worm. What the West would dismiss as metaphor or superstition was something entirely different in Japan: a system. A coherent map of the human interior, drawn with the only tools available at the time. The tools have changed. The map turned out to be astonishingly accurate.

Spies inside your body

It all began in China, with the Daoist concept of sānshī (三尸, lit. “three corpses”) or sānchóng (三蟲, “three worms”). According to the earliest sources – including Ge Hong’s treatise Baopuzi from the fourth century CE – every human being is born with three demonic parasites inside their body. The first lives in the head and feeds on the temptation of gluttony. The second sits in the chest and thrives on greed. The third occupies the belly and fuels lust. Together they form an internal sabotage operation: they initiate diseases, invite other harmful forces into the body and – most critically – keep a running log of their host’s transgressions.

The mechanism was precise and bureaucratic in a way any official of the Japanese shogunate would recognise. Every sixty days, on the night corresponding to the Chinese cyclical day gēngshēn (庚申), when a person fell asleep, the three worms would leave the body, ascend to heaven and present their report to a divine functionary bearing the title Sīmìng (司命, “Director of Destinies”). On the basis of that report, a set number of days was subtracted from the host’s lifespan. Daoist adepts pursuing immortality therefore had not only to lead a virtuous life but also to actively fight their own worms: through fasting (to starve the upper one), meditation and renunciation (to weaken the middle one), and celibacy (to defeat the lower one). Or more simply: stay awake on gēngshēn night, so the prisoners cannot snitch.

This belief reached Japan in the ninth century, during the Heian period, and immediately found fertile ground. The court aristocracy adopted it with the same enthusiasm they brought to every Chinese refinement. The monk Ennin, visiting China in 838, noted in his diary that the custom of staying awake on kōshin night was widespread there – “just as it is at New Year’s in our country.” In the Muromachi period the warriors took up the tradition. And in the Edo period, kōshin-shinkō (庚申信仰, “kōshin faith”) spread to ordinary people and became one of the most enduring elements of Japanese folk religion.

From private fear grew a social institution. Kōshin-machi (庚申待, “waiting for kōshin”) – all-night vigils held every sixty days – became an excuse for neighbourhood gatherings called kōshin-kō. People assembled in the evening, ate, drank sake, sang, recited sūtras, played board games. The rule was simple: as long as nobody in the room falls asleep, the sanshi cannot escape from anyone. An all-night vigil with friends was quite literally an act of metaphysical self-defence. The worms, trapped inside, had to listen to the laughter and the clinking of cups, helplessly noting down fresh transgressions on their celestial scrolls.

After three years of regular vigils, a group would erect a stone stele called a kōshin-tō. Thousands of these steles still stand across the Japanese countryside today – by roadsides, in thickets, at temple gates. Many of them bear the figure of Shōmen Kongō (青面金剛) – a fearsome, blue-skinned, many-armed deity who tramples jaki (邪鬼) – small evil spirits – and keeps the sanshi themselves in check. And at the feet of Shōmen Kongō there almost always sit three monkeys: one covering its eyes, one its ears, one its mouth. Mizaru, Kikazaru, Iwazaru – see not, hear not, speak not. The Three Wise Monkeys, which the whole world associates with some vague “Eastern wisdom,” are in fact the guardians of a cult devoted to worms living inside the human body. Their job is to make sure no sin reaches where it should not.

A bestiary of the interior

In 1568, while Europe was living through the Reformation and the dead of generations lay on the battlefields of Japan’s sengoku era, someone in the town of Ibaraki near Osaka was compiling a bestiary of a different kind. A physician known as Nisuke produced a manuscript entitled “Harikikigaki” (針聞書, lit. “Records of Listening with the Needle”) – a handbook of acupuncture and medicine containing sixty-three colour illustrations of creatures living inside the human body. Each creature – a mushi – was assigned to a specific organ, specific symptoms, specific emotions and a specific treatment. The manuscript survived the centuries and is today an exhibit at the Kyushu National Museum in Fukuoka. It has never been fully translated into English. Most research on it exists only in Japanese.

Reading the descriptions of individual mushi, it is hard not to notice that the author – however fantastical the creatures he drew – was observing real people with real ailments and trying to understand them using the only concepts available to him. Kanshaku (肝積, lit. kan = liver + shaku = accumulation), an angry creature with human arms, dwelt in the liver and “violently thrust itself upward toward the chest cavity.” Its host screamed with rage, sought outlets for energy and craved sour foods. In traditional Chinese medicine the liver is the organ of anger – so kanshaku was a literal embodiment of anger. Not a metaphor for anger. An embodiment: something alive, something separate from the person in whom it dwelt.

Other mushi were equally specific. Haishaku (肺積) – a creature in the lungs that triggered sadness and an aversion to smells. Haimushi (肺虫), another “lung worm,” allegedly fed on rice and could transform into a hitodama – a phosphorescent flame floating at night above cemeteries. Kishaku (気積) liked fatty food and fed on fish and birds; treatment with tiger stomach was recommended. The most peculiar was Koseu (コセウ, written in katakana, without kanji, as though even the scribe did not know where this creature came from): a worm in a hat, with a long white beard and the body of a snake. The hat protected it from medicine – nothing could reach it. It liked sweet amazake and caused its host to grumble incessantly.

The most dangerous of all sixty-three was Kakuran no mushi (霍乱の虫) – a black-headed, red-bodied creature that caused violent vomiting and diarrhoea, symptoms resembling cholera. But the “Harikikigaki” was not limited to terrifying diagnoses. There was also Gyūkan (牛疳) – a worm taking the form of a cow, settled in the lungs, which became active during meals: it sensed food in the throat and grew so wildly excited that its host fainted. There were also disturbingly mundane creatures: Hizō no mushi (脾臓の虫, “spleen worm”) caused dizziness and the sensation of being struck on the head, as though someone had hit you with an invisible fist. Each of these worms had a specific appearance – the illustrations in the manuscript are colourful, detailed and surprisingly expressive, as though the author knew each one personally. Some look like deformed insects. Others resemble miniature dragons. Still others are hybrids: half-bird, half-snake, with human arms and a grimace on their snout.

It is worth adding that mushi in Edo culture were not confined to medicine. In 1788, Kitagawa Utamaro – the ukiyo-e master known above all for his portraits of beautiful women – published an album called “Ehon mushi erami” (画本虫撰, “The Picture Book of Selected Insects”), in which he combined precise studies of insects and plants with erotic kyōka poems. This was not a medical textbook – it was a work of art in which insects served as metaphors for human desires and relationships. Mushi in Japanese culture were not exclusively a source of fear and illness. They were also a source of fascination, a poetic image, a mirror in which a person examined their own interior.

It would be tempting to dismiss all of this as an outlandish curiosity. But the “Harikikigaki” does something that no medieval European treatise on bodily humours does: it creates a systematic psychosomatic model in which emotion, organ, diet and therapy form a closed circuit. Sadness is linked to the lungs and an aversion to smells. Anger is linked to the liver and a craving for sour flavours. This is not a random collection of superstitions – it is an attempt to build a coherent map of the human interior, using the tools a sixteenth-century physician had at his disposal. He had no MRI, no biochemistry, no concept of neurotransmitters, and above all no scientific method and no generations of scientists before him. He had a needle, herbs and observation. And from those three things he built something that we perceive today as a fantasy containing astonishingly accurate intuitions.

The worm in the child

Of the entire mushi bestiary, one species has survived to our times in virtually unchanged form: kan no mushi (疳の虫). The kanji kan (疳) denotes a paediatric disease associated with digestive disorders and malnutrition – but in practice the term expanded to cover everything modern parents would call a “difficult child.” Colic, crying fits, night waking, irritability, hyperactivity, biting people, nail-biting, bloating, loss of appetite, fevers with no visible cause. Traditional Japanese kampō (漢方) medicine did not blame the child. It blamed the worm.

This seemingly minor shift of responsibility had profound consequences. A child with kan no mushi was not “bad” or “unruly” – it was infected. It was treated, not punished. The main method of therapy was shōnishin (小児鋝, lit. “children’s needle”) – a specifically Japanese form of paediatric acupuncture in which no needles are inserted; instead, the child’s skin is gently rubbed with rounded metal instruments, stimulating specific zones of the body. The therapist diagnosed the child through touch: searching for subtle changes in temperature, texture and skin tension. The treatment was gentle, non-invasive and – perhaps surprisingly – is still practised in Japan today (alongside scientific medicine, not instead of it).

A comparison with the Western history of dealing with “difficult children” is instructive. In eighteenth-century Europe, a hyperactive, irritable, disobedient child had a “bad nature” that needed to be straightened out with discipline. Pastoral treatises on child-rearing recommended the rod. Nineteenth-century medicine introduced the concept of “nervousness.” The twentieth century brought more labels: minimal brain damage, hyperkinetic syndrome, and finally ADHD. Every one of these labels located the problem in the child. Japanese kan no mushi – with its fantastical trappings of worms and needles – did something radically different: it located the problem outside the child. The child was not the source of the trouble. Something in the child – something alien, something that was not the child – was causing the suffering. And since the culprit was a creature, the child deserved compassion and treatment, not punishment.

The psychologist Richard Schwartz, creator of Internal Family Systems therapy, would say that Japanese physicians with their mushi had intuitively made the same move he proposed in the 1980s: they separated the person from their symptoms. You are not bad. A part of you – or, in the language of Edo, a worm inside you – is behaving in a way that causes you trouble. And that part can be worked with.

One more thing: the term kan no mushi lives on in everyday Japanese. When a Japanese mother says her toddler has kan no mushi, she does not mean an actual parasite. She means the same constellation of symptoms that the “Harikikigaki” described five hundred years ago: unexplained crying fits, irritability, sleep problems, constant dissatisfaction. The diagnosis sounds archaic. The empathy behind it – “the child is not bad; something inside it won’t let it rest” – is remarkably modern.

The worms that stayed in the language

The bestiary has been forgotten. The stone kōshin steles are growing over with moss. But mushi live on – in the language. A modern Japanese person, who has probably never heard of the “Harikikigaki” and could not name a single one of the sixty-three worms, uses them daily in speech without realising that they are repeating a thousand-year-old psychological theory.

腹の虫がおさまらない

Hara no mushi ga osamaranai

“The worm in the belly won’t calm down.”

Meaning: I am so angry I cannot control myself. Note the construction: it is not me who fails to master my anger. The worm inside me refuses to settle. The subject of the anger has shifted: the emotion has a will of its own, independent of the speaker.

虫の居所が悪い

Mushi no idokoro ga warui

“The worm is in the wrong place.”

Meaning: someone is in a bad mood, irritable. Again: it is not the person who is irritable. The worm inside has shifted to somewhere it shouldn’t be. A bad mood is the consequence of something beyond the speaker’s control.

虫唆が走る

Mushizu ga hashiru

“The worm’s saliva runs.”

Meaning: disgust. Literally: the worm in your innards is so revolted that it salivates, and you feel that saliva as a wave of physical revulsion. Disgust here is someone else’s act – performed by the creature within.

虫の知らせ

Mushi no shirase

“A message from the worm.”

A premonition that something bad is about to happen. A vague feeling that I should phone my grandmother, and then it turns out she has just been taken to hospital. The Japanese word for intuition is literally a communiqué from a creature inside.

To these we can add compound words that turn people into worm habitats:

- nakimushi (泣き虫, “crying worm”) – a crybaby,

- yowamushi (弱虫, “weakness worm”) – a coward,

- hon no mushi (本の虫, “book worm”) – a bookworm (strikingly similar to the English word).

In each of these expressions, a person does not so much display a trait as serve as its “residence.” A crying worm lives inside you. A fear worm occupies your body. You are not a coward – you carry a cowardice worm within you. This is a radical shift of perspective, entirely natural in Japanese but lost in translations of films, anime, games and literature.

Polish knows something similar. A “worm of conscience” („robak sumienia”) gnaws from within. “Doubts consumed him” („zjadały go wątpliwości”) – doubts as living creatures with teeth. And the Latin re-mors – remorse – literally means “biting again.” The intuition that a person’s interior is not unified, that forces with their own will inhabit it, is probably older than any civilisation.

Ninety per cent of happiness is produced in the intestines

Let us now move from sixteenth-century Osaka to a modern laboratory. In 2015, Elaine Hsiao’s team at Caltech published a study in “Cell” that changed the way neuroscience thinks about emotions. They discovered that gut bacteria directly influence serotonin production in the intestines – and the intestines produce as much as ninety to ninety-five per cent of all serotonin in the human body. Five per cent is produced in the brain. The rest – in the visceral darkness, among a hundred trillion microorganisms whose existence we are unaware of when we eat lunch and wonder why we feel sad.

Before we conclude that all we need to do is look after our gut to be happy, a caveat is needed. Gut serotonin physically cannot reach the brain regions that regulate mood. Happiness does not flow from belly to brain. But the gut communicates with the brain by other routes – through the vagus nerve, through the immune system, through chemical substances produced by bacteria that enter the bloodstream. John Cryan and Ted Dinan of University College Cork, authors of groundbreaking research on the gut–brain axis, coined the term psychobiotics – bacteria that influence mental health. As Emeran Mayer writes in his book “The Mind-Gut Connection”: the brain and gut carry on an unceasing conversation, most of which we never hear. We hear only the consequences: anxiety, irritability, sadness – or their absence. Giulia Enders writes engagingly about this topic in her book “Gut: The Inside Story of Our Body’s Most Underrated Organ.”

The net result? Science does not say: “happiness is born in the belly.” Science says something subtler and in a sense more unsettling: trillions of organisms live in your intestines and, via multiple chemical pathways, influence whether you feel anxiety, sadness, irritability or calm. You are not aware of this. You have no direct control over it. They do not know you exist. You do not know they exist. And yet your mood is partly their product.

The author of the “Harikikigaki” would nod in approval.

A soul transplant

The strongest evidence that “worms within” genuinely help shape personality comes from experiments involving faecal transplants in mice raised in completely bacteria-free conditions. These animals, growing up in sterile bubbles, have never encountered a single microorganism. And they behave differently from normal mice: they exhibit disrupted social behaviour, altered anxiety levels and dysfunctional stress responses. They live in a body devoid of passengers – and their psyche knows it.

In 2011, a team from McMaster University in Canada conducted an experiment that should be remembered by anyone interested in the human mind. The researchers took two strains of mice with different “personalities”: BALB/c, naturally anxious, and NIH Swiss, naturally bold. They transplanted the gut microbiota from these mice into a third group: germ-free mice that had no bacteria of their own. The result: mice that received bacteria from the anxious donors became anxious – regardless of their own genetic strain. Mice with the bold donors’ microbiota became bolder. Behavioural traits – what we would colloquially call temperament – transferred along with the bacteria.

This was not an isolated finding. Later experiments went further. Transplants from the intestines of people suffering from irritable bowel syndrome accompanied by anxiety – given to germ-free mice – produced a measurable increase in anxious behaviour in those mice. Transplants from people with depression induced depression-like behaviour in the mice. In 2021, something even more surprising was demonstrated. Researchers studied mice living in a social hierarchy – dominant and submissive. Both groups had different gut microbiota. When bacteria from the submissive mice were transplanted into germ-free recipients, the recipients adopted not only submissive behaviours but also changes in the way their bodies stored fat. Gut bacteria simultaneously shaped behaviour and metabolism – as though personality and physiology were a single package.

In 2021, a team from Caltech went a step further: they identified the specific pathway by which the absence of gut bacteria alters behaviour. Mice without a microbiome had elevated levels of stress hormones – and as a result avoided contact with other mice. When they were given bacteria from healthy individuals, the hormone levels dropped and the mice began to behave sociably. The worm did not fly to heaven to inform the deity. But trillions of worms were sending a chemical signal to the brain that said: “be afraid” or “don’t be afraid.” “Approach others” or “keep your distance.”

The language of the sixteenth-century Japanese physician was metaphorical. The mechanism turned out to be literal. Mushi govern our mood – only they have different names, live in the intestines instead of the liver, and communicate with the brain via the vagus nerve instead of flying to heaven at night.

We do not have a single “self” – and we never did

Mushi are more than a premonition of the gut–brain axis. They are a premonition of something deeper: that the human “self” is not unified. That what we call personality consists of many voices, many forces, many agents with partly contradictory aims. The Japanese did not need Freud to know this. They had mushi.

Take Freud’s id, ego and superego. Three psychic agencies, each with different aims, locked in constant conflict. The id wants immediate pleasure. The superego demands moral perfection. The ego tries somehow to negotiate between them. Compare this with the three sanshi: the head worm (gluttony, temptation), the chest worm (greed, hoarding) and the belly worm (lust, carnality). Three internal forces, each pulling the person in its own direction. Three agencies, none of which is “you,” each of which lives inside you and influences your decisions.

But the most striking convergence is with the contemporary therapy called IFS (Internal Family Systems), created by Richard Schwartz in the 1980s. Schwartz was working with patients with eating disorders who described their experience in terms no textbook accommodated: they spoke of “parts” of themselves. “A part of me wants to eat. A part of me hates that I eat. A part of me panics when I think about food.”

Schwartz, instead of treating this as a symptom of pathology, took it literally. He built a therapeutic model in which the mind is naturally multi-part – composed of “managers” (parts that control, plan and maintain order), “firefighters” (parts that react impulsively to crisis, for instance through addiction or withdrawal) and “exiles” (wounded, deeply hidden parts that carry pain, shame and loneliness). Behind them all stands the “Self” – the core of the personality, which is calm, compassionate and curious.

Schwartz knew nothing about Japanese mushi. But had he encountered them, he would have recognised something immediately: Japanese folk medicine had been doing for centuries what he was trying to do in the therapist’s office. It separated the person from their emotions, gave internal forces specific names, located them in the body and proposed methods for calming them. Anger was not “your” anger. It was the action of kanshaku, a creature in the liver. Fear was not “your” fear. It was the murmur of mushi no shirase. The expression hara no mushi ga osamaranai – “the worm in the belly won’t calm down” – is in many respects identical to an IFS patient saying: “this part of me won’t calm down.”

Buddhism adds yet another layer. The concept of anattā (muga, 無我 – “not-self”) holds that a permanent, unified “self” is an illusion – that what we call personality is a shifting constellation of mental phenomena, none of which is permanent and none of which is “really you.” Within this philosophy, saying that your emotions belong to worms rather than to you does not sound like superstition. It sounds like common sense. Emotions are not you. They are something that passes through you. You can observe them, name them, watch their movement – just as you might observe a worm in a jar. But you do not have to identify with them.

This may be the most important lesson in the entire history of mushi. The point was not that worms literally exist. The point was something far more significant: a daily, language-embedded, culturally ingrained practice of de-identification from one’s own emotions. A Japanese speaker who said “hara no mushi ga osamaranai” was not saying “I am furious.” They were saying: “something inside me is furious.” And that small grammatical difference is a psychological chasm. Because if the worm is furious, then I do not have to be furious. I can observe the anger, watch it dispassionately and let it go when it chooses to go.

The worms you cannot see

There is something moving about the image of those people sitting at night in a wooden house on the outskirts of Edo, watching over one another to make sure nobody falls asleep. Their cosmology was fantastical. Their zoology – invented. Their pharmacology – questionable (tiger stomach cures nothing). And yet at the very core of their system lay something that modern science is arriving at step by step, cautiously, publication by publication: that organisms live inside the human body and influence who we are. That emotions are not wholly “ours.” That something inside us operates with its own aims and its own logic.

Perhaps the most enduring legacy of the Japanese physicians of Edo is not any specific diagnosis or any specific treatment. It is something more delicate: the habit of speaking about emotions in the third person. The habit of treating anger, fear, sadness and disgust not as oneself but as something that resides within you and can be named, located and – with a little patience – calmed.

Six centuries of kōshin-machi taught the Japanese something that Western psychotherapy has been teaching for forty years: that you do not have to be your emotions. That you can observe them from a distance. That whatever inside you screams, gnaws, grumbles and keeps you awake has the right to exist – but does not have to define you.

The worms are there. They always were. It is not clear whether they can ever be removed – or whether that would even be a good idea. In the meantime, we must somehow live with them. And every sixty days, make sure we do not fall asleep.

SOURCES

1. Ge Hong, Baopuzi (抱朴子), 4th century CE – Daoist treatise containing a description of the sanshi (三尸) concept.

2. Kōhn, Livia, “Laughing at the Tao: Debates Among Buddhists and Taoists in Medieval China”, 1995

3. Arthur, Shawn, “Early Daoist Dietary Practices: Examining Ways to Health and Longevity”, 2013

4. Schwartz, Richard C., “No Bad Parts: Healing Trauma and Restoring Wholeness with the Internal Family Systems Model”, 2021.

5. Yano, Jessica, “Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis”, Cell 161, 2015

6. Wu, Wei-Li, “Microbiota regulate social behaviour via stress response neurons in the brain”, Nature, vol. 595, 2021

7. 針聞書の世界 – ハラノムシの研究 (Harikikigaki no sekai – Hara no mushi no kenkyū), exhibition catalogue, Kyūshū National Museum, 2006.

8. Cryan, John F. & Dinan, Timothy G., “Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour”, Nature Reviews Neuroscience, vol. 13, 2012

"Strong Japanese Women"

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    未開    ソビエライ

 An enthusiast of Asian culture with a deep appreciation for the diverse philosophies of the world. By education, a psychologist and philologist specializing in Korean studies. At heart, a programmer (primarily for Android) and a passionate technology enthusiast, as well as a practitioner of Zen and mono no aware. In moments of tranquility, adheres to a disciplined lifestyle, firmly believing that perseverance, continuous personal growth, and dedication to one's passions are the wisest paths in life. Author of the book "Strong Women of Japan" (>>see more)

Personal motto:

"The most powerful force in the universe is compound interest." - Albert Einstein (probably)

  Mike Soray

   (aka Michał Sobieraj)

未開    ソビエライ

 An enthusiast of Asian culture with a deep appreciation for the diverse philosophies of the world. By education, a psychologist and philologist specializing in Korean studies. At heart, a programmer (primarily for Android) and a passionate technology enthusiast, as well as a practitioner of Zen and mono no aware. In moments of tranquility, adheres to a disciplined lifestyle, firmly believing that perseverance, continuous personal growth, and dedication to one's passions are the wisest paths in life. Author of the book "Strong Women of Japan" (>>see more)

Personal motto:

"The most powerful force in the universe is compound interest." - Albert Einstein (probably)

Mike Soray

(aka Michał Sobieraj)

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