Revealing mistake: During the Mutants' escape, while they're attacking others in the Citadel some of their rubber bald caps come loose, and we can see the caps' edges over their hair/heads.
Beyond the Time Barrier (1960)
1 revealing mistake - chronological order
Directed by: Edgar G. Ulmer
Starring: Arianne Ulmer, Boyd 'Red' Morgan, Darlene Tompkins, Robert Clarke, Stephen Bekassy, Vladimir Sokoloff
Genres: Sci-fi
Visible crew/equipment: When Colonel Martin walks into the OR while the doctor and nurse are examining Major Allison, the boom mic can be seen moving around behind the overhead surgical lighting, at the top of the screen.
The Supreme: You are from a nation of speaking people. How glorious that must be! Our society is less fortunate.