A missionary in Africa realizes that the one thing he has never taught the natives is how to speak English. He takes the chief for a walk in the forest. He points to a tree and says to the chief, "This is a tree". The chief looks at the tree and grunts, "Tree".
The missionary is pleased with the response. They walk a little farther, and the missionary points to a rock and says, "This is a rock." Hearing this, the chief looks and grunts, "Rock".
The missionary is really getting enthusiastic about the results, when he hears a rustling in the bushes. As he peeks over the top, he sees a couple of natives in the midst of heavy sexual activity. The missionary is really flustered, and quickly says, "Riding a bike".
The chief looks at the couple briefly, he pulls out his blowgun and poisoned darts, and kills them.
The missionary goes ballistic, and yells at the chief that he has spent years teaching the tribe how to be civilized and kind to each other, so how could he kill these people in cold blood that way?
The chief replied, "My bike".