What concepts in the Sawi culture intrigued / reviled / saddened / angered / surprised me?

The most astonishing idea in the novel was probably the practice of cannibalism. Though I knew that the Sawi were primitive and barbaric people, I never thought that they would actually consume human flesh.
To be honest, I never believed that there were people who eat human flesh. Human being, I thought, was instinctively repulsive to eat human flesh. After I read this book, however, I found myself too narrow-minded. If people believe in ideas of river spirits and resurrection (except Jesus Christ) that have practically no reliability, why wouldn't some people believe in the seemingly least reasonable thing in the world?
Don Richardson describes cannibalism on page 33:

"Meanwhile Maum began excavating the brains from inside the skull by way of the
opening he had forced. His friends brought leaves and wooden platters of various
kinds to collect their share of the brains, to be eaten with the flesh when it
was cooked. Maum himself would not eat of the brains."

This showed how cruel and organized the Sawi people are, just like we are about some traditions like marriage. The point is that they strongly believe in their traditions that they merely take it granted. Although we are the same human beings, it's astounding to see how different we are from other cultures, with distinct rituals and beliefs.