What did Mafatu‘s grandfather wear that showed him to be a brave man?

As well as needing to kill the wild boar because he's hungry, Mafatu's also desperate to prove his bravery, to prove that he's a man and not a boy. In doing so, he will seek to emulate the courageous deed of his grandfather, Ruau, who once killed a wild boar himself, earning the undying admiration and respect of his people. Grandfather Ruau made himself a necklace from the teeth of the animal, which he wore with pride, and which became a symbol of his courage. Mafatu plans to do the same. His reputation among his people is less than impressive. If he's to follow in the footsteps of his father, the Great Chief, then he's going to need to perform a truly heroic deed, and that means killing a wild boar. Making himself a necklace out of the boar's teeth will be a tangible symbol of his bravery, just as it was for his grandfather.