What does the part in which Marlow wonders why the savages (30 to 5) do not eat them tell us about the narrator's attitude towards it and the world?
It is the part which begins when he says:
"why in the name of all gnawing devils of hunger they didn't go for us - they were thirty to five - and have a good tuck-in for once, amazes me now when i think of it."
What does it tell us about the world depicted in the novel an Conrad's attitude towards it?
First of all, Marlow is surprised that even though the cannibals have run out of food, they do not attack and eat the white men aboard the boat--amazing, he thinks, because the cannibals definitely outnumber the whites. What he comes to realize is that the cannibals demonstrate restraint, a quality he greatly admires, a quality he did not expect to find in "savages." Ironically, these cannibals show restraint, but the "civilized" whites do not. When the boat is attacked, the whites fire their guns wildly into the bush, even though they don't see any targets. Their actions are reminiscent of the shots fired by the French warship that Marlow witnessed on his journey to the Congo, just useless little pops of gunfire shot into the leafy greenness of the shore where there was no evidence of any native life. The foolishness and panic of the whites coupled with their lack of restraint contrasts them sharply with the cannibals, who maintain a dignity not seen in the whites on Marlow's boat.
This reversal of Marlow's expectations is just another of his learning experiences during his time in Africa. Although his original intent was simply to pilot a boat on the Congo, he gradually learns more about the whites in Africa and about the "savages" than he had ever expected. As a European, he came to Africa with preconceived notions about Africa; he discovers, however, that some of the natives, represented here by the cannibals, are more "civilized" in some respects than the whites. Conrad emphasizes this reversal with his reversal of the typical use of black and white imagery. The city of Brussels, for instance, where the main office of the ivory company is located, is described as a "whited sepulchre." Ivory itself, which the white "pilgrims" seem to "worship," is white and leads to the downfall of such "universal geniuses" as Kurtz. Marlow's whole worldview is so changed that he is willing to lie to Kurtz's Intended even though he declares he hates lying because it's like "biting into something rotten." His experience with the cannibals is just another in the series of events that reshape his view of the world.