Yuan-tsung Chen, an author, leaned forward in an oversize velvet chair to tell the story of the man so hungry that he ate himself. Once, that tale had seemed unbelievable to her. “I thought that was an exaggeration,” she said. But living in a village during the Great Leap Forward, Mao Zedong’s calamitous attempt to catapult China into communist plenty in the late 1950s, changed her view on what extreme hunger could drive people to actually do.