In English, the word ‘animal’ applies to both humans and non-human animals; in Indonesian, the word (‘hewan’) does not apply to humans. In this study, English and Indonesian speakers made yes/no class-inclusion judgments for statements about animals. An interesting pattern was found among Indonesian (but not English) speakers: 9-year-olds agreed that mammals are animals and denied that humans are either mammals or animals (logically consistent), while adults agreed that humans are mammals and that mammals are animals but denied that humans are animals (logically inconsistent). Further, English-speaking children were more likely than Indonesian-speaking children to agree that mammals are animals and that humans are mammals. We suggest that (a) the Indonesian naming practice may have consequences for children’s acquisition of the hierarchical relationships between HUMAN, MAMMAL, and ANIMAL, and (b) the apparent decline in logical consistency among Indonesian speakers may reflect a conflict between categorical knowledge and well-established naming practices.