In this paper we examine the role of animals in orthopaedic surgery and research in the 1960s. We describe their different roles as patients and laboratory models in the emergence of two new biomedical objects that we call "implant-pets" and "bone-sheep." For this purpose, the ways of practicing (veterinary) orthopaedic surgery and of "materializing," or bringing into being, complex and heterogeneous biomedical objects are analyzed as the coevolving histories of humans and animals. Focusing on non-discursive material practices, we use the (...) concept of "articulation" in order to explore the inventive and intervening character of biomedical practices that led to the existence of implant-pets and bone-sheep. Our analysis interprets the distribution of human-like and animal-like character features and values to these animals not as the result of a stable animal-human boundary, but as the effect of diverse interactions in contingent historical situations. This dynamic—relational approach makes it possible to investigate the drawing of human-animal boundaries in the making and thus contributes in a new way to the study of animal-human relationships in history. (shrink)