Which sentence best indicates the story's message or theme?

Now Beavers are much afraid of Bears, who break down the beaver dams so as to let off the water, catch them, and eat them.
Porcupine often visited Beaver in his house, which is dry and comfortable, and unfortunately annoyed his host by leaving some of his quills there.
Beaver contrived to explain the whole thing as a joke, and the pair appeared to be on as good terms as ever.
We are also told that it is on account of this happening that people who have loved each other very much sometimes quarrel and are no longer friends.