Variation in folk knowledge of biological kinds among members of a single ethno-linguistic community has long been a focus of ethnobiological attention and interest. Concentrating on variable local understandings of animal names, this paper discusses three forms of binary names applied to animal categories among the Nage of Flores Island, eastern Indonesia. It is shown that while some people, the "lumpers," regard such names as unproductive binomials designating terminal taxa (folk-generics or folk-specifics), others, the "splitters," construe the same names as composite terms comprising separate names of two distinct subtaxa. In two of the three cases evidence from the animal nomenclatures of related languages supports the splitters. Also discussed are factors possibly accounting for this variation, including age, gender, and variable familiarity with local fauna bound up with ecological change.