For thousands of years Jewish law was based on revelation and precedent. God's will, as revealed in scripture, was determinative: it demarcated what was permitted, required and prohibited. A contemporary rabbi could offer only a slight emendation of precedents. The early modern period, however, witnessed a dramatic shift in Jewish norm-making. A new source of knowledge, empirical evidence, became both valid and persuasive. Indeed, it could even override both revelation and precedent. What is so fascinating about this watershed moment in Jewish norm deliberation is that it spawns from an ancient concern about zoonotic diseases arising from pigs.