In order to infer a theme from a story ,one must identify the central _ and its _

The central idea and its supporting details because the central idea is the main idea of the story. The supporting details are your evidence of the central idea. 

Central conflict and its resolution. The conflict and resolution reflects to how the story revolves as a whole. 

The details that best show evidence of tribal traditions are, "never in the history of his people had a man married a woman who spoke a different tongue” and "it has never been heard," was the verdict of an old man speaking a few weeks later.