“A lie can travel halfway around the world while the truth is putting on its shoes”. This oft-misattributed quote highlights a persistent problem in our world. Why do false ideas spread so easily? Sure, blame people’s ignorance or stupidity, but philosophers Cailin O’Connor and James Owen Weatherall write that the problem is far more insidious. Through a combination of case studies and modelling work, they convincingly argue that the same social dynamics by which truth spreads are inherently vulnerable to exploitation. But first, some vegetable lamb.