What Exactly is a Sum Xu?

This article aims to resolve the academic debate over the identity of the mysterious animal Sum Xu described in Michał Boym’s Flora sinensis. Through examining various Chinese sources published in the seventeenth century and the vocabulary they used to characterize creatures belonging to the Rodentia and Carnivora orders, the essay demonstrates that the animal at stake was most likely a weasel (Mustela), either Siberian (M. sibirica) or Japanese (M. itatsi), and that it was commonly known under the name song shu, even though in modern Mandarin this term is reserved for the squirrel. Additionally, the article investigates methodological problems arising from studying the import of Chinese terminology into the European context and suggests that scholars should consider the unstable linguistic diversity of Ming China when discussing the transfer of knowledge from the East to the West in the early modern period.