Documentaries. I saw footage of a new tribe that was either in new Zealand or the amazon. It was funny watching them shoot arrows at the plane. Most likely they'll introduce "the silver roaring bird" into their religious lore.

Then they aren't undiscovered. And if they seek God, he will reveal himself and then they can choose whether or not to worship him.

They were undiscovered till then. Right now your being difficult. For the record, no human contact was actually made with that tribe because it could be dangerous to expose them to our technology and modern sicknesses. Who knows. Their immune systems might not be able to combat a common cold. So you're saying that a people who already have their own answers to everything will discover God if they decide to look for him, even if there is nobody to educate them about him? [spoiler]the benefit of religion is that sometimes you can make irrational claims that can't be reasoned with. They only require belief. [/spoiler]

Actually, if there is a God that wants to be known, he will make it happen. He can reveal himself however and wherever he wants.