The first aspect that I noticed in this story and even in the title is the explanation of how the rattlesnake learned to bite. The foremost important reason for this story is the explanation. The snake needed some kind of way to protect itself from people that were annoying him because he had no way to be assertive. Since he needed some way of protecting himself he went to the Elder Brother who gave him fangs to bite anyone who annoyed the snake.
The second aspect of the story is the lesson of it and what the story is trying to teach. To me the story is don't push someone so far that they have to give themselves the upper hang and could eventually do harm to someone because of the pent up aggression that they feel. The snake eventually goes to the Elder Brother to get help because people have annoyed him so much about his rattler. He is too nice to say anything about it so when the Elder Brother gives him fangs he uses them to hurt and eventually kill the first person that annoys him after getting his fangs.