Astronauts on Mars are terrorized by an unseen enemy.
"Troper, get back to your vehicle!"
- Chromosome Casting: This is one of two Outer Limits episodes with all-male casts ("The Chameleon" is the other).
- The Film of the Book: It's based on a 1955 short story by Jerry Sohl.
- In Name Only: Sohl did the first draft of the script and is the only writer credited. However, multiple revisions (none of them by Sohl) led to many changes, although the basic plot of the original story is retained.
- Sand Is Water: The creatures on Mars "swim" beneath the surface of the sand.
- Token Minority: Captain Johnson is one of the earliest African-American astronauts depicted on American television, although Lt. Willowmore from "Nightmare" and Lt. Travers from "Moonstone" got there first.