In 1822, a point-blank musket blast left Alexis St. Martin with a permanent open hole into his living stomach. What followed was one of the most unbelievable, and ethically troubling, chapters in medical history, as a frontier army surgeon used that window to discover how human digestion actually works.

This episode traces the partnership between St. Martin, an illiterate Canadian voyageur, and Dr. William Beaumont, exploring the groundbreaking science and the deeply uncomfortable power dynamics between a doctor and his human guinea pig. The knowledge they produced underpins everything we know about gut health today.

• How a catastrophic shotgun wound healed into a gastric fistula when St. Martin's stomach fused to his skin, sealing off fatal infection
• Beaumont's roughly 200 experiments over a decade, dangling food on silk  ...