"Once when various tropical diseases had laid low almost every 'agent' in the station he was heard to say, 'Men who come out here should have no entrails.' He sealed the utterance with that smile of his as though it had been a door opening into a darkness he had in his keeping."

As Marlow reflects on the Manager’s character and general lack of leadership skills, he cites this line and suggests that his success in the job stems from the fact that he is never ill. This notion of “hav[ing] no entrails” carries a significant double meaning, one which speaks to the “darkness” referenced in the following sentence. The Manager, of course, says that the men at the station “should have no entrails” so that they do not succumb to foreign diseases. This line, however, also reflects the moral emptiness necessary to survive in such a corrupt occupation.

"But the wilderness had found him out early, and had taken on him a terrible vengeance for the fantastic invasion. I think it had whispered to him things about himself which he did not know, things of which he had no conception till he took counsel with this great solitude—and the whisper had proved irresistibly fascinating. It echoed loudly within him because he was hollow at the core...."

After recounting his initial discussions of Kurtz with the Russian Trader, Marlow offers his listeners his own interpretation of Kurtz and his relationship to his work. Marlow suggests that the wildness Kurtz experienced, or the lack of expectations to follow, elicited and encouraged the man’s worst qualities. This opportunity to satisfy devilish temptations with no personal risks becomes irresistible to Kurtz, primarily because he lacks morals and substance. The metaphorical echoing of whispers ensures that Kurtz succumbs to their call over and over again.

"The shade of the original Kurtz frequented the bedside of the hollow sham whose fate it was to be buried presently in the mould of the primeval earth." 

Once Kurtz is aboard the ship headed back to Europe, Marlow observes his patient’s internal struggles as he nears death. His discussion of “the shade of the original Kurtz” and the “hollow sham” of a man that lies before him suggests that he has reached an even deeper level of emptiness. Not only is Kurtz morally bankrupt, emphasized by the darkness associated with the word “shade,” but death renders him devoid of his entire identity. Describing him as “the hollow sham,” an object, highlights his complete loss of humanity, and the word “sham” specifically suggests that the dying man is not an accurate representation of who Kurtz truly is.