Though Willis H. O'Brien gets top special-effects billing, Ray Harryhausen actually did 85%-90% of the stop-motion animation for this film, although the animation is based on O'Brien's designs and storyboards.
Second-unit director David Sharpe recalled an incident that happened on the nightclub set: "We were shooting some action stuff . . . which featured lions, tigers, elephants, and apes in cages around the table area. We had trained lions to run from one side of the set to the other. One of them broke loose, jumped onto the top of his cage and grabbed the trainer by the throat. I was in the camera cage. I pushed the iron door open, raced across the set and punched the lion in the face. I guess I shocked him so badly he let go, turned tail and ran into his cage."
The version of this shown on TCM features the burning orphanage sequence overlaid with an orange filter for dramatic effect, just as it had been in its original 1949 release.
When Joe smashes through the facade during the nightclub riot, the first scream you hear is that of Fay Wray, stock audio from the original King Kong (1933), which was also produced by RKO.