How does Marlow feel when he encounters the howling and dancing tribesmen outside Kurtz' station in Heart of Darkness?
This scene takes place during the night before Marlow and his men evacuate Kurtz from his hellish station in the heart of the jungle. While it's difficult to know exactly what's going through Marlow's mind at this point, it's possible to assume that in this moment, Marlow truly believes that he has stumbled upon the "heart of darkness."
Conrad's image of the tribesmen in the forest after Kurtz is taken away is probably one of the most disturbing images in the book. The shapes of the figures in the woods take on a nearly hellish aspect, and so it's accordingly possible to interpret this moment as a metaphorical representation of the depraved, devilish lifestyle Kurtz has devoted himself to. Indeed, it's possible to assume that the scene in the woods is a personification of a "heart of darkness," and specifically Kurtz' heart of darkness.
In making this claim, it's important to recognize the potentially racist undertones of Conrad's metaphor. While Conrad certainly spends much of the novella criticizing white colonialism, it's also important to recognize that he uses the black natives as a representation of the primitive and depraved instincts at the heart of human nature. Unloading this assumption onto a particular race is troubling, as it attempts to argue that black Africans are closer to the primordial beginnings of humanity than whites. As such, it's important to carefully weigh Conrad's work, recognizing its artistic merits alongside its racially-charged baggage.