This Podcast Will Kill You

Ep 200 Poop Part 1: How the sausage gets made

February 10, 2026

Key Takeaways Copied to clipboard!

  • Human poop is composed of approximately 75% water, with the remaining 25% biomass being up to 55% bacteria, highlighting the significant role of the gut microbiome in waste composition. 
  • Dung beetles and other decomposers are essential ecological heroes, transforming animal waste into nutrients that fertilize soil and cycle resources, as demonstrated by the crisis caused in Australia when native beetles could not process cattle dung. 
  • The process of digestion involves specialized muscular contractions called peristalsis and the regulated release of material through multiple sphincters, culminating in the colon where water is reabsorbed to form solid stool over a period of 24 to 72 hours. 
  • Animal scat provides a wealth of information about diet, health, and environment, with carnivores generally producing less, cylindrical scat containing hair or bone, while herbivores produce more, floatier scat with plant material. 
  • Certain animal feces, such as Kopi Luak (civet coffee) and ambergris (sperm whale rectal mass), are highly valued commodities used in food and perfume, respectively. 
  • The massive increase in global livestock populations has led to a 'poop catastrophe' where excess domestic animal waste, often contaminated with pesticides toxic to decomposers like dung beetles, disrupts crucial ecological nutrient cycles. 

Segments

Host Personal Poop Story
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(00:07:07)
  • Key Takeaway: A fifth-grade field trip led to an embarrassing, prolonged incident of soiling pants during a walk to a planetarium.
  • Summary: One host recounted an embarrassing childhood memory of losing control of their bowels while walking to an outdoor education facility’s planetarium show. The host continued to let waste pass, committed to reaching the destination despite the resulting mess in their denim jeans. The incident concluded with a desperate attempt to clean the soiled pants in the shower afterward.
Introduction to Poop Episode
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(00:05:21)
  • Key Takeaway: This episode of This Podcast Will Kill You, Part 1, focuses on the composition of poop and the mechanics of its creation.
  • Summary: The hosts decided to dedicate a two-part miniseries to the topic of poop, starting with the biological processes involved. This first installment will cover what constitutes poop, the process of digestion that creates it, and examples from the animal kingdom. The subsequent episode will address ‘poop problems’ and the history of sanitation.
Human Digestion Process Walkthrough
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(00:10:35)
  • Key Takeaway: Digestion begins in the mouth with enzymes and mechanical breakdown, proceeding through the esophagus via peristalsis, and into the stomach where food becomes chyme.
  • Summary: Food breakdown starts immediately in the mouth with salivary amylases and chewing, then moves down the esophagus using muscular contractions called peristalsis, passing through the lower esophageal sphincter into the stomach. The stomach churns the food with acid and enzymes like pepsin, turning it into a liquid mass called chyme, which is slowly released through the pyloric sphincter.
Small Intestine Function and Structure
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(00:13:58)
  • Key Takeaway: The small intestine, despite its name, is 9 to 16 feet long and is the primary site for nutrient absorption, aided by secretions from the gallbladder and pancreas.
  • Summary: The stomach regulates the slow release of chyme into the small intestine, which is crucial because this organ performs almost all nutrient absorption. Digestive enzymes from the pancreas and gallbladder finalize the breakdown of starches, proteins, and fats into absorbable components in the duodenum and jejunum. The final section, the ileum, is specialized for absorbing essential nutrients like Vitamin B12 and bile salts.
Large Intestine and Poop Formation
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(00:18:33)
  • Key Takeaway: The large intestine (colon) is wider than the small intestine and is the primary location where leftover chyme is converted into formed stool through massive water and electrolyte reabsorption.
  • Summary: The colon’s main function is absorbing one to two liters of water daily, which solidifies the liquid chyme into formed feces, aided by muscular peristalsis. The colon houses a distinct and abundant microflora that helps break down final food bits and produces essential vitamins like K and B vitamins. The final exit involves the rectum and the anal canal, controlled by two sphincters: one involuntary (internal) and one voluntary (external).
Poop Composition and Transit Time
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(00:24:13)
  • Key Takeaway: The time required to form a stool ranges widely from 24 to 72 hours, and the consistency is classified by the Bristol Stool Scale, where types 3-5 are considered ideal.
  • Summary: While stomach emptying takes 1 to 4 hours, the entire process of forming a turd takes one to three days, influenced by factors like fiber intake and medications such as GLP-1 agonists. The Bristol Stool Scale categorizes consistency from Type 1 (separate hard lumps) to Type 7 (pure liquid), correlating harder stools with longer transit times. Fiber aids transit by holding water and providing bulk for the colon to peristals against.
Poop as Building Blocks of Life
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(00:33:52)
  • Key Takeaway: Poop is fundamentally composed of water (about 75%) and biomass (about 25%), with bacteria making up a massive portion of that solid mass, underscoring its role as recycled biological material.
  • Summary: Beyond water, the solid portion of feces is largely biomass, with up to 55% of that being bacteria, many of which are still alive. These microbes are vital for breaking down undigested material and synthesizing necessary vitamins like K and B vitamins for host absorption. Therefore, labeling poop merely as ‘waste’ ignores its composition of essential building blocks like carbon, nitrogen, iron, and calcium.
Etymology and Animal Poop Names
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(00:34:57)
  • Key Takeaway: The word ‘poop’ likely originates from an onomatopoeic Middle English word related to the sound of a horn or fart, contrasting with words like ’excrement’ which relate to separation or sifting.
  • Summary: Various terms for feces exist, such as ’excrement’ (to separate out), ‘crap’ (residue from rendered fat), and ’turd’ (torn off the body). The word ‘poop’ is thought to derive from the Middle English ‘poopin,’ an onomatopoeia for a horn sound that evolved to mean fart, then poop. Animal waste has specific names like ‘scat’ for wild animals and ‘guano’ for bat/bird droppings.
Ecological Value of Poop
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(00:40:05)
  • Key Takeaway: Poop is a rich, nutrient-packed substance that serves as a vital resource for numerous organisms, including dung beetles, flies, and soil microbes, transforming ‘waste’ into opportunity.
  • Summary: In tropical rainforests, human feces are quickly removed by over 50 species of dung scarabs, demonstrating how waste is a treasure for decomposers. The economic contribution of dung beetles to the US beef industry alone was estimated at $380 million annually by 2006 for their work in nutrient cycling and parasite control. This illustrates the principle that what one organism produces as waste, another views as essential for survival, reproduction, or resource acquisition.
Poop Shape and Pooping Duration
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(00:49:17)
  • Key Takeaway: Despite vast differences in diet and size, researchers found that the duration of defecation across many species, from elephants to rabbits, clusters around a ‘magic number’ of 12 seconds, facilitated by intestinal mucus.
  • Summary: Poop shape varies significantly across species, such as the cube shape of wombat scat versus the cylindrical shape of carnivore scat. However, modeling across species suggests that the time taken for the feces to exit the anus is remarkably consistent at 12 seconds, plus or minus seven seconds. This consistency is attributed to the lubricating effect of mucus lining the intestines, which ensures smooth passage regardless of the volume or animal size.
Scat as Informational Gold
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(00:56:00)
  • Key Takeaway: Poop shape, size, and contents reveal significant details about an animal’s diet, species, and physiological state.
  • Summary: Poop is an informational pile of gold, allowing observers to deduce an animal’s diet (e.g., fish vs. squirrels) and health status (e.g., stress or parasites). Carnivore scat is typically cylindrical and contains hair or bones, while herbivore scat is more voluminous, floatier, and contains plant material. Rabbits produce two types of feces: visible hard pellets and softer, nutrient-dense pellets eaten immediately in their dens.
Coprophagy and Nutrient Reabsorption
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(00:58:01)
  • Key Takeaway: Animals practice coprophagy (eating feces) for nutrient reabsorption, predator concealment, or to refresh gut microbiota during illness.
  • Summary: Many animals, including rabbits, mice, and cows, consume their own or others’ offspring’s feces. This behavior serves to re-extract nutrients, conceal evidence of offspring from predators, or potentially refresh the gut microbiota, especially in cases like cows experiencing intestinal disease. This practice is not unique to small mammals.
Prized Fecal Products
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(00:58:55)
  • Key Takeaway: Feces from specific animals yield extremely valuable substances, such as Kopi Luak coffee and ambergris used in high-end perfumes.
  • Summary: The most expensive coffee in the world, Kopi Luak, is made from beans passed through a palm civet’s bowels. Ambergris, a hardened mass of fecal material and undigested squid beaks from about 5% of sperm whales, is a highly valuable substance used as a fixative in perfumes. A large piece of ambergris found in 1914 was valued at the equivalent of $4.5 million today, leading to theories that whales may die from the blockage.
Diverse Uses of Poop
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(01:04:00)
  • Key Takeaway: Beyond consumption, feces are utilized as fuel, insulation, fertilizer, building material, paper, and for forensic DNA testing.
  • Summary: Poop has numerous practical applications, including being used as fuel, insulation, insect repellent, and fertilizer. Elephant dung can be processed into paper, with one elephant producing enough material for 115 sheets daily. Fecal DNA testing has even been used in criminal investigations to match dog feces at a crime scene to residue on a suspect’s shoe.
Ecological Roles and Human Impact
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(01:05:08)
  • Key Takeaway: Poop is vital for ecological functions like seed dispersal and nutrient redistribution across boundaries, but human factory farming overwhelms natural cycles.
  • Summary: Ecologically, poop is critical for nutrient redistribution via organisms like dung beetles and animals that cross aquatic/terrestrial boundaries, and whale feces help offset ocean acidification. However, the sheer volume of waste produced by humans and exponentially increased livestock (e.g., chicken population grew from 3.9 billion in 1961 to 29 billion in 2023) creates a ‘poop catastrophe.’ This excess waste, often containing toxic pesticides excreted by livestock, prevents natural nutrient cycling and threatens decomposer populations.
Shifting Perspective on Waste
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(01:09:04)
  • Key Takeaway: The goal of the two-part series is to shift the perspective on feces from a public health concern to recognizing its value as a resource.
  • Summary: The hosts aim to approach poop from a perspective beyond typical public health concerns like contaminated water supplies. Listeners are encouraged to suspend disgust and view feces as a hugely valuable substance rather than mere waste. The next episode will cover historical and future waste management solutions.
Further Reading and Sources
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(01:10:03)
  • Key Takeaway: Several books and scientific papers offer deeper dives into the science, history, and ecology of feces.
  • Summary: Recommended reading includes books like Eat, Poop, Die: How Animals Make Our World by Joe Roman and The Origin of Feces by David Waltner Toes. Scientific literature cited includes papers on the ecological functions of dung beetles and a review on characterizing feces for advanced treatment technology. The hosts encourage listeners to check the podcast website for full source lists.