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In 1970s Thailand a woman sentenced to death survived a firing squad aimed at the left side of her chest because her heart was on the right. This episode explains situs inversus, found in about 1 in 10,000 people, in which the internal organs are mirrored. In the total form the heart sits on the right, the liver and gallbladder on the left, the stomach and spleen on the right, and even the lungs swap their three and two lobes. Because the organs still connect correctly, most people are healthy: NBA player Randy Foye, Donny Osmond and Catherine O'Hara all have it, and Rose Marie Bentley of Oregon lived to 99 without knowing.

The cause traces to weeks four to six of gestation, when cilia on the embryo sweep fluid leftward to set the body's axis. When they fail, as in primary ciliary dyskinesia, organ placement becomes a 50/50 coin flip. The hosts cover Kartagener syndrome, the dangers of partial reversals such as isolated levocardia and heterotaxy, how surgeons fit a standard donor heart into a mirrored chest, and an unexpected rise in cases in China after a COVID-19 wave.

• Appendicitis in a mirrored patient causes pain in the lower left abdomen, which can mislead doctors
• Isolated levocardia, about 1 in 2 million, carries a 95 percent rate of severe congenital heart disease
• Surgeons build baffles from synthetic grafts or the patient's own pericardium to route blood into a donor heart
• A 2004 study found normal rates of left handedness, but a 2023 replication found 26 percent against 10.6 percent in the general population
• The China cases followed maternal infections during the four to six week window when cilia set organ placement

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Picture a red apple and rate it from one, photo vivid, to five, nothing at all. Those who see nothing may have aphantasia, the absence of a mind's eye. In 1880 Francis Galton asked distinguished scientists to picture their breakfast table, and many insisted mental imagery did not exist. In 1897 Théodule Ribot described a physiologist who saw the printed word dog instead of a dog. Interest returned in 2005 when Adam Zeman met Patient MX, who lost his imagery after minor surgery, and Zeman's team named congenital aphantasia in 2015.

Most aphantasics cannot summon images on purpose but still dream in pictures. A March 2021 study found they showed no sweat response to a scary story, though they reacted to frightening photos like everyone else. They struggle with detailed visual recall but do well on spatial memory, and many also lack an inner voice, which researchers named anauralia in 2021. Yet Pixar co-founder Ed Catmull, Disney animator Glen Keane, Firefox co-creator Blake Ross and The Martian author Andy Weir all have it.

• A 2022 screening estimated 0.8 percent of people have no visual imagery and 3.9 percent only dim imagery
• Catmull surveyed 540 Pixar colleagues and found production managers visualized more vividly than the artists
• Aphantasics are slower at hidden object searches because they check a mental list of features
• Science writer Lynne Kelly uses memory palaces through spatial memory rather than pictures
• A 2024 University of Plymouth program improved imagery in most athletes after six weeks

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When Karen Keegan needed a kidney transplant, DNA tests on her sons showed she was not their biological mother. She was a tetragametic chimera: two fertilized eggs had fused in her mother's womb, so her blood carried one genome and her reproductive organs another. This episode explains whole body chimerism, clues such as Blaschko's lines that appear under certain UV light, and microchimerism, the cells mothers and fetuses exchange during pregnancy. It describes a 2010 case of a 40 year old man with a scleroderma-like illness whose female cells came from a vanished twin.

The hosts then turn to the animal kingdom: marmoset twins who share blood and can carry each other's reproductive cells, male yellow crazy ants that need two unfused genomes, merged sponges and half colored budgerigars. Plants follow, from grafted fruit to variegated houseplants, along with a 2012 RNA and DNA hybrid virus found in Boiling Springs Lake in Lassen Volcanic National Park. The episode ends with lab chimeras and the ethical question of how many human cells make an animal human.

• About 95 percent of fraternal twin marmosets trade blood through fused placentas
• The 1600s Bizzarria fused the Florentine citron and the sour orange
• Beatrice Mintz made the first chimeric mice in the 1960s, followed by a goat and sheep geep in 1984
• Researchers made a sheep whose blood was 15 percent human in 2007
• A 2023 study reported a chimeric monkey with up to 92 percent donor derived cells in tested tissues

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Forty-five years before Helen Keller, Laura Bridgman became the first deafblind person famous for learning English. Born in 1829 in Hanover, New Hampshire, she lost her sight, hearing, smell and taste to scarlet fever at age two, the same illness that killed her two older sisters. A hired hand named Asa Tenney gave her her first tactile signs. In October 1837 she went to Samuel Gridley Howe's Perkins Institution for the Blind in Boston, where Howe and matron Lydia Drew taught her with raised letter labels on spoons and keys, then loose letters, then a finger alphabet traced into her palm.

Charles Dickens praised her in American Notes in 1842, and crowds came on Saturdays to watch her. Then her support vanished: Drew left to marry, Howe took a 15 month honeymoon with Julia Ward, and teacher Mary Swift left in 1845. At 16 Laura's weight fell from 113 to 79 pounds, and she recovered on a visit home in 1846. In the early 1880s she shared a cottage at Perkins with a young Anne Sullivan, who learned the manual alphabet from her before going to teach Helen Keller.

• Her father stamped on the floorboards to get her attention through vibration
• She learned arithmetic on a metal board with square holes and type in under three weeks
• Howe and Swift clashed over her religious instruction, Unitarian against Congregationalist
• She begged to follow teacher Sarah White to the Sandwich Islands as a housekeeper and was left behind
• Kate Keller sought help after reading Dickens on Laura, and Sullivan brought Helen a doll whose clothes Laura had sewn

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Born Jerri Lin Cahill near Salem, Ohio, Jerri Nielsen became an emergency physician and mother of three, then after a divorce signed on in 1998 as the doctor at the Amundsen-Scott South Pole Station. During the 1999 winter, with temperatures around minus 76 degrees Fahrenheit and no flights until spring, she found a lump in her breast. Guided by doctors in the United States over slow satellite email, she biopsied herself, but the outdated supplies gave inconclusive results.

On July 11 an Air Force C-141 Starlifter from Christchurch, New Zealand flew over in total darkness and parachuted six bundles onto a drop zone lit by burning fuel barrels. With new ultrasound equipment Nielsen biopsied herself again and the slides confirmed breast cancer. She started hormone therapy and chemotherapy, training station mechanics and scientists to place IVs by practicing on potatoes and fruit. An LC-130 Hercules evacuated her on October 15. She went on to write the bestseller Icebound and speak widely before her death in June 2009 at 57.

• Why a plane could not land in winter: skis freeze to the ice, jet fuel gels and hydraulic fluid freezes
• The precedent of Leonid Rogozov, the Soviet doctor who removed his own appendix in Antarctica in 1961
• The station sits above 9,000 feet, adding thin air to her fight
• Susan Sarandon starred in a TV movie of her story, and House based an episode on it
• The cancer returned in 2005, yet she kept traveling, including trips back to Antarctica

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Sleepwalking, or somnambulism, is not acting out a dream. This episode explains it as state dissociation: the motor and navigation systems wake while the prefrontal cortex, which handles memory and judgment, stays in deep N3 slow wave sleep. Freud tied it to unconscious wishes in 1907 and a 1954 study blamed repressed hostility, but sleep recordings showed it happens in non-REM sleep, unlike REM behavior disorder. Sleepwalkers' eyes are open, with a glassy stare and dilated pupils. One sleepwalking parent gives a child a 45 percent chance, two parents 60 percent, and about 5 percent of children sleepwalk regularly against roughly 1.5 percent of adults.

In children, sleep apnea can trigger episodes, and removing enlarged tonsils often ends them. In adults, stress, sleep deprivation, serotonin differences and drugs such as zolpidem play a part. The hosts cover sleep eating, sexsomnia and how sleepwalking differs from an alcohol blackout. Then come the courts: an 1846 acquittal in Boston, a 1963 ruling by Lord Morris, the 1992 Canadian Parks case, and defenses that failed.

• People with migraine or Tourette syndrome sleepwalk at four to six times the general rate
• Episodes can track the premenstrual phase, while pregnancy often suppresses them
• Fruit fly research on the transcription factor AP2 links sleep consolidation with early brain development
• A 2001 defendant who said he was fighting ostriches had told his son not to turn on the lights
• Scott Falater changed clothes and hid the weapon in a Tupperware container, steps the court found incompatible with deep sleep

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For roughly two thousand years, mainstream medicine taught that a woman's womb could roam her body. This episode traces the idea to Greek gynecological texts credited to Hippocrates and to Plato's Timaeus, which described an unfruitful womb growing angry and blocking the breath. In the second century CE Aretaeus of Cappadocia called it an animal within an animal, and doctors tried to herd it home with scent: perfumes and myrrh below, burning hair or sulfur under the nose. Soranus of Ephesus mocked the theory, and Galen held the uterus was stationary, blaming retained substances that released harmful fumes.

Galen's correction changed the theory but not the treatments. In 1603 English physician Edward Jorden published The Suffocation of the Mother, the first English text on the subject, tying the condition to fits, laughing and crying. He testified in the 1602 bewitching case of 14 year old Mary Glover, who accused Elizabeth Jackson of witchcraft, arguing her symptoms were natural. The episode follows the idea into Freud's conversion disorder and its removal from the DSM-III in 1980.

• Older scholars placed the theory's origin in ancient Egypt, a claim modern analysis rejects
• Soranus used the Greek word for wild beast to ridicule the idea that the womb flees bad smells
• Jorden was brought in by the Bishop of London amid a fight over Puritan exorcisms
• Aristotle's view of women as emotionally variable helped justify limits on education and public life
• The episode links the history to modern findings that women's pain is more often dismissed as psychosomatic

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In 1961 physician Walter Kennedy coined the word nocebo, Latin for I shall harm, to describe harm that comes from a patient's expectations of an inert treatment rather than from any drug. This episode explains how anticipating pain triggers the release of cholecystokinin, which amplifies pain signals, and why there is no evidence of a gullible personality type. The numbers are striking: a 2022 meta-analysis of COVID-19 vaccine trials attributed 72 percent of adverse effects after the first dose in the placebo groups and 52 percent after the second to the nocebo effect.

The hosts look at the 2013 statin scare in the United Kingdom, when media coverage of side effects led many patients to stop their medication and was followed by an estimated 2,000 additional cardiovascular events. They cover dropouts from placebo arms of Parkinson's and depression trials, electromagnetic hypersensitivity, theories about Havana syndrome, and culture bound curses such as pointing the bone. The episode ends with the ethical bind doctors face when informing a patient can itself cause harm.

• Almost 9 percent of Parkinson's patients and 1 in 20 depression patients quit trials while taking inert pills
• In 1973 G. W. Milton at Sydney Hospital described melanoma patients who declined and died soon after hearing their prognosis, comparing it to bone pointing
• Stewart-Williams and Podd argue that placebo and nocebo can describe the same mechanism, such as immunosuppression, judged good or bad
• Framing helps: 95 percent of patients tolerate this drug instead of 5 percent get joint pain
• Authorized concealment lets patients consent in advance not to be told about mild side effects

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Every air breathing vertebrate studied has some version of the mammalian diving reflex, and infants up to about six months can often survive underwater longer than adults. This episode explains the trigger: cold water on the face around the nose and eyes while holding the breath. The trigeminal nerve signals the brainstem, the vagus nerve slows the heart, and rising carbon dioxide, which turns to carbonic acid in the blood, sets off the carotid bodies. In people the heart rate drops 10 to 25 percent while vessels in the limbs clamp shut to keep oxygenated blood flowing between heart and brain.

Seals take it much further, slowing from around 125 beats per minute to as low as 10, kept going by an elastic aortic bulb, a spleen that squeezes stored red blood cells into circulation, and muscles packed with myoglobin. The hosts then turn to the Sama Bajau sea nomads, whose enlarged spleens are linked to variants in the PDE10A gene, and Korea's Haenyeo women divers of Jeju. The episode closes on the toll diving takes on the human body and why splashing cold water on your face can calm a racing heart.

• Immersion diuresis: blood pushed into the chest stretches the heart, which releases atrial natriuretic peptide and sends you looking for a bathroom
• Diving can trigger ectopic beats and ST depression as the vagus nerve and soaring blood pressure pull against each other
• Diving mammals also carry neuroglobin and cytoglobin to protect brain tissue
• The Haenyeo show unusually strong heart slowing and cold tolerance
• Physician Edmund Goodwyn described diving bradycardia in humans in 1786

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Some blind people play basketball, mountain bike and skateboard with no technology at all, using sharp tongue clicks and the echoes that come back. This episode explains active human echolocation: why a palatal click works better than a hum, and how the returning echo tells the brain an object's location, size and density, so that a wooden fence sounds duller than a metal one. In 1749 Denis Diderot described blind people sensing silent objects, and for centuries this was called facial vision, thought to be skin feeling air pressure, until experiments at Cornell in the 1940s showed that blocking the ears made the ability disappear. Donald Griffin coined the word echolocation in 1944.

A 2014 fMRI study by Lore Thaler recorded echoes inside expert echolocators' ear canals and played them back in the scanner. In the experts the echoes lit up the primary visual cortex, while untrained sighted volunteers showed no visual activity. The episode then follows Daniel Kish, who lost both eyes to retinal cancer at 13 months and built the FlashSonar method, Ben Underwood, who rollerbladed and played street football by clicking, and Lucas Murray, a British boy taught by Kish after his parents saw Underwood on television.

• The precedence effect: sighted brains suppress echoes because the eyes already map the room
• Kish long resisted the white cane, then combined it with echolocation in what he calls perceptual mobility
• His charity World Access for the Blind takes blind teenagers mountain biking and hiking
• Underwood lost his eyes at three, taught himself to click by five, and died of cancer in 2009 as a teenager
• Kish taught Lucas Murray the basics in four days, and by seven Lucas could identify materials by sound