Bioethicists often defend novel practices by drawing analogies with practices that we are already familiar with and currently tolerate. If some novel practice is less bad than some widely-accepted practice, then (it is argued) we cannot rightly reject it. Using the bioethics literature on xenotransplantation and interspecies blastocyst complementation as a case study, I show how this style of argument can go awry. The key problem is that our moral intuitions about familiar practices can be distorted by their seeming normality. (...) When considering the ethics of emerging technologies and novel practices, we should remain open to the possibility that our moral views about familiar practices are mistaken. (shrink)