It’s been 40 years since Alien was first released, and it’s as fresh and frightening today as it was in 1979. That’s thanks in large part to its genre nonconformity, which set it apart not only from other science fiction but from other horror as well. Alien was hardly the first horror movie to mash up with sci fi – or the first sci fi to include horror elements – but the two work together so well in Ridley Scott’s space terror, not only by being faithful to both genres, but also by flipping on tropes and traditions.