As our referenced quote states in SFMZ's Sci-Fi Subgenres A to Z feature, horror and and science fiction seem to go hand in hand. Horrific Sci-Fi is closely linked to the 'horror' genre, and while it's often bloody, science is crucial to each premise. Films such as zombie movies can be a toss up where they are sorted. Many zombies films are straight up horror with a minor element of sci-fi.
For example, Night of the Living Dead 1968 has a line of dialogue regarding a returning probe from Venus carrying a virus that infected the dead. The rest of the film really has no science fiction aspects. It's really a toss up whether they should be sorted in SFMZ's Horror section or our Horror Sci-Fi section. So I spread the wealth, you can see more zombie movies in SFMZ's Horror section. The fifties horror sci-fi films listed below are featured in SFMZ's Fifties Sci-Fi section.