For years people have speculated how the light circle animation was made. The magazine "Science and Invention" suggested at the time that fluorescent lights were used as a purely practical effect, moved up and down manually on invisible wires by stage hands. In later years Lang said in interviews that a brightly lit steel ball used as a pendulum was filmed or photographed with a long exposure time in front of a black screen and was then composited onto the image, though this is not consistent with the multiple exposure method used.