A missionary who had spent years showing a tribe of natives how to farm and build things to be self-sufficient gets the word that he is to return home.
He realizes that the one thing he never taught the natives was how to speak English, so he takes the chief and starts walking 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 padre points to a rock and says, "This is a rock." Hearing this, the chief looks and grunts, "Rock." The padre 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 in the midst of heavy sexual activity.
The padre is really flustered and quickly responds, "Riding a bike."
The chief looks at the couple briefly, pulls out his blow gun and kills them.
The padre 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 just kill these people in cold blood that way?
The chief replied, "My bike."