This chapter addresses the ontological concerns in John Carpenter's In the Mouth of Madness (1995) by focusing on its radical aesthetic and philosophical disorientations: the non-linear presentation of time, cyclical narratives and visual repetition, and the fundamental distrust of perception. Parallels between the existential preoccupations of In the Mouth of Madness and The Matrix (1999) have already been drawn. Both The Matrix and In the Mouth of Madness work with the exciting dramatic potential of the idea that reality is not an absolute that can be reliably perceived, it is something we agree upon collectively, adding in a dash of malevolence to Cartesian scepticism — what if some external, evil force were constructing the veil of reality upon which duped masses then agreed upon? Crucially, though, Carpenter does not create a crusading action film that re-installs a sense of stable, authentic reality once this veil has been lifted, as the Wachowskis did. Instead, he crafts a more obtuse, surreal cinematic vision of what might be called Cartesian paranoia — crucially, a horror film.