I think bkoganbing has written the most perceptive and accurate review of this film, of all the postings here. Bkoganbing's detailing of the history of the Belgian Congo, from its inception as a private fiefdom of King Leopold, to its transformation into an official "colony," in 1907, is exactly right. And the placing of this film in a 1950s context is also important to point out, as that reviewer has done. When this film was made, the later Zaire/Congo was still a Belgian colony, with independence still a few years away. The makers of the film were no doubt influenced by the prevailing attitudes of the time, and, considering some of those attitudes, the movie is fairly progressive, I think.
I lived in the Congo in the late 1970s, when it was called Zaire. That was 70 years after the time period of this story, but some of the elements in this film were still in existence when I was there. Most villages had chiefs, of some form or other, and many had what we used to call "witch doctors." A fair number of people believed that these doctors had special powers, and acted accordingly. Drums were/are still used as a form of communication- what used to be called the "bush telegraph." People dressed as most modern people do- T-shirts and sneakers being quite common- but some of the traditional beliefs still held sway. I'm not an expert in Congolese traditional customs and ceremonies, but I was able to observe a number of interesting things while I was there. Experts in the subject could critique this film's depiction of these things far better than I could. But the scenes in the film seemed fairly accurate, to me, especially for the 1907 time period. Though I would stand corrected, if need be.
I was impressed that they seemed to get the language right. Mitchum says that they are speaking Chiluba, which is in fact one of the major languages of the Congo. There are four major trade languages there- Chiluba, Lingala, Kikongo, and Swahili. These trade languages are used as large regional languages, in different parts of the country, so that people can communicate with one another. Swahili in eastern Congo (and neighboring countries), Lingala in the north, and along some rivers, Kikongo in central areas, and Chiluba in the south-- roughly speaking (and if memory serves correct). There are hundreds of smaller regional and tribal languages, and, while many people can speak five or ten of these languages, they often use one of the four trade languages when in another area. The old colonial Belgian French is still one of the government languages, and many people speak that as well. I spoke French and Kikongo when I was there, in my capacity as a volunteer aid worker. Many of my Congolese/Zairean friends spoke multiple languages (to my shame, as I struggled with just these two). Anyway, I think Mitchum and the others are really speaking Chiluba. I didn't speak that language, but all these languages have some overlapping vocabulary, and I think it was Chiluba, or something like it. Again, another poster may be more knowledgeable than I. It seems that Fox must have done some homework for this picture. Mitchum, too, as he handles himself impressively well with the language. I'd love to read comments by Mitchum on his memorizing that dialogue! Mitchum, one of my favorites, was always a trouper, I think.
As many have pointed out, he and Hayward never actually went to the Congo. The studio did a pretty good job, I think, of blending studio sets with location shots. Though, as is usually the case, you can spot which are which. Though at least the studio sets aren't as obvious as in many films. The location shots sure brought back memories to me. The river steamers, dugout canoes, riverfront towns, etc.- all looking the same in the '70s, when I was there. The most obvious studio intrusion, to me, was the gorilla you see at the beginning of the film. Though it isn't as bad as many Hollywood "gorillas" you often see- Charlie Gemora in an ape suit, etc., it still detracts from the story. But this IS a 60 year-old film, so it's best not to be too critical, I guess. For its time period, they got some things pretty right. Especially considering that this was not made as a documentary, but as a Mitchum-Hayward entertainment picture, with fictional elements. As one poster pointed out, the source material was a serious book detailing the experiences of two nuns, who tried to bring western medicine to the Congo. Quite a morph there. But still not as outrageous as one might expect from the sensationalistic title. And better and more authentic than lots of other films Hollywood made about Africa, in those days. In my humble opinion, anyway.