The internet has lots of disturbing things on it. But this has to be right at the top of the list:
The Tradition of Infanticide
The tradition is based on beliefs that babies with any sort of physical defect have no souls and that others, such as twins or triplets, are also "cursed".
The Brazilian authorities turn a blind eye to infanticide, out of respect for the tribal culture.
Imagine if these Aboriginal Brazilians wrote a bible today. It might even resemble the Old Testament. God was OK with stonings and murder and sacrifice. The New Testament was definitely OK with Jesus sacrificing himself.
But this goes back to the fact that we evolved a susceptibility to believe in the supernatural.
Man is superstitious by nature. Our ancestors, who probably resembled the tribe in the film, couldn't explain lightning, so they had to make up supernatural causes and buy into them, in order to not go crazy. Faced with self awareness and knowledge of mortality, all sorts of weird ideas could then be put into cultural rituals to appease their God or Gods, and avoid death for at least a while, or make sure that they'll be taken care of after they die.
Surely, their God is not the Abrahamic God, yet they still have a concept of a God who can curse them and give them bad luck if they don't perform rituals that they obviously made up....well they had to make them up, unless one believes that God went to Brazil and gave them the go ahead to bury babies.
Can you believe that this stuff still goes on in the year of 2008? I do. After all, even in a progressive province like Ontario, we still have prayer in the Legislature.