This paper is an examination of the horror elements found in Peter Watts’ Blindsight. In depicting an encounter with aliens, this science fiction novel explores topics such as the nature of sentience, mankind’s relationship with technology, posthumanism, and the limitations of the human body and mind. Blindsight also envisions entities (aliens, vampires, and artificial intelligences) capable of interacting with material realities inaccessible to human beings. Using Levi R. Bryant’s machine-oriented ontology, this thesis demonstrates how Watts employs these themes and issues to problematize anthropocentrism and the notion of selfhood. These elements—and more—will be discussed and shown to match the criteria associated with ontological horror.