Looping Lines: The entire movie was filmed without sound, and so virtually all the actors had to loop their dialogue after filming was complete, with a couple of exceptions:
Kien Shih (Han) spoke no English, so his voice was dubbed by Chinese-American actor Keye Luke.
When the extended Cantonese/Mandarin versions were released for the first time in English in 1998, some extra dubbing had to be done, because no English dialogue existed at that time for those scenes. One of the scenes involved Roy Chiao (Shaolin Abbott) and Bruce Lee. Chiao was still alive (he died shortly thereafter), and was able to dub himself, but Lee's voice was supplied by Bruce Lee biographer John Little. Luckily, Lee's real voice was left alone for the scenes that originally used it.