Horror is about the violation of boundaries. To keep life tolerable we parcel up the world in our head, organising experience into handy categories, and the most familiar genre icons signal their disruption: alive/dead (zombies, Frankenstein’s monster), old/new (The Mummy), reality/dreams (Freddy Krueger), animal/man (werewolves). The puss and blood and inside-out, syrupy mess of body horror speaks to a primal fear about the loss of identity and self. Roman Polanski’s 1968 horror classic Rosemary’s Baby, adapted from Ira Levin’s hugely popular novel and screening in the Beanbag Cinema tonight, is organised around a series of boundary violations. Some of these…