Buy exactly 100 birds for exactly 100 coins: pigeons at 5 for 3, sārasa cranes at 7 for 5, swans at 9 for 7, peacocks at 3 for 9. Mahāvīra set this puzzle in 850 CE — and near-identical "hundred fowls" problems appear in 5th-century China (Zhang Qiujian), 8th-century Europe (Alcuin's puzzles for Charlemagne's court), and the medieval Islamic world. One indeterminate-equation puzzle, dressed in local birds, circulating the whole medieval world — mathematics as a traveling folk-tale, and one of the clearest traces of how problems moved between civilizations.