Greg and Patrick talk about internal validity -- broadly and traditionally -- but also as an increasingly important lens through which to view our information-saturated world, and be responsible, critical, and skeptical members of scientific communities as well as society. Along the way, they also mention gargling bleach, 5G cell towers, vaping lysol, fecal transplants, the problem with firetrucks, Star Trek and causality, Sherlock Holmes, melon-wrapped prosciutto, kitty physics, the regression fairy, tails-challenged individuals, and Mad Eye Moody.