At approx 38:08 an alien is taking measurements and you hear him saying something. It was "The readings are...25,26 to the right...27,28,29 to the left...30,31 up...32,33 down." played in reverse.
Contrary to the usual practice in the 1950s, the credits appear at the end rather than at the beginning of the movie.
Just over 40% of this film is stock footage
The bulging eyeballs of the aliens were thought by many to have been made out of ping-pong balls. Makeup artist Harry Thomas revealed that these eyes were actually made from the bottoms of egg cartons.
The image of the alien city with the flying vehicles that Denab shows Martin is the underground Martian city from Flight to Mars (1951).