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"A voice! a voice! It was grave, profound, vibrating, while the man did not seem capable of a whisper. However, he had enough strength in him—factitious no doubt—to very nearly make an end of us, as you shall hear directly." (3.11)
Kurtz may look like a skeleton/ ghost/ phantom/ dying man, but he still has enough power in him to almost do away with Marlow and his crew.
"At this moment I heard Kurtz's deep voice behind the curtain: 'Save me!—save the ivory, you mean. Don't tell me. Save me!'" (3.18)
Kurtz is so debauched by greed that he assumes everyone feels the same way. He believes that the manager does not actually want to save him, but to save the ivory in order to look good to the Company. He is, of course, correct.
[Kurtz]: "'Sick! Sick! Not so sick as you would like to believe. Never mind. I'll carry my ideas out yet—I will return. I'll show you what can be done. You with your little peddling notions - you are interfering with me. I will return.'" (3.18)
Kurtz—apparently ignoring the fact that he is literally dying—still thinks he's going to win. He considers not only that the manager himself is less powerful than he, but that the manager's ideas are merely "little peddling notions" beside his own great ambitions.