Monster a Go-Go! stops rather than ends. Director Bill Rebane abandoned the science fiction horror film in 1961 after running out of money, and Herschell Gordon Lewis picked it up in 1965 to pair with one of his own movies as a double feature. By that time the original cast were unavailable to complete the filming, so Lewis had to make do with what he had, which led to some awkward moments. At the end, as scientists are closing in on the radioactive monster that has replaced astronaut Frank Douglas, it suddenly disappears and a narrator says:

As if a switch had been turned, as if an eye had been blinked, as if some phantom force in the universe had made a move eons beyond our comprehension, suddenly, there was no trail! There was no giant, no monster, no thing called ‘Douglas’ to be followed. There was nothing in the tunnel but the puzzled men of courage, who suddenly found themselves alone with shadows and darkness! With the telegram, one cloud lifts, and another descends. Astronaut Frank Douglas, rescued, alive, well, and of normal size, some 8,000 miles away in a lifeboat, with no memory of where he has been, or how he was separated from his capsule! Then who, or what, has landed here? Is it here yet? Or has the cosmic switch been pulled? Case in point: The line between science fiction and science fact is microscopically thin! You have witnessed the line being shaved even thinner! But is the menace with us? Or is the monster gone?

What does this mean? None of it is explained. Lewis called his film a parody, but Rebane called it “the worst picture in the world.”