While body modification might generally seem to take the form of denaturalizing a biological given, this article looks at the same practice as normalizing the always already unstable corpus. The dominant discourse of the post-Enlightenment relies on the notion of the centrality of the individual subject within the singular and separate body, where distinctions between self and other are secure. Against this the incidence of monstrosity in general, with its disordered crossing of the boundaries of the proper, offers a gross (...) insult. I look in particular at instances of conjoined twinning to demonstrate that the body can only be regarded as one by a process of material and discursive modification, which nonetheless finally fails to efface the trace of the monstrous other that frustrates the closure of the self-same. (shrink)