How does Marlow describe the cannibals when he talks about why he hired them?

The cannibals are the grunt crew of Marlow's ship, and they are the only group of natives who ever voice any kind of statement or opinion to the whites. Marlow is surprised at their tranquil manner, and he seems to respect them. Marlow notes that they brought hippo meat for food but, when it goes rotten, they restrain from eating the pudgy white pilgrims.