Final answer:
The simile 'the earth rose and fell like a great animal breathing' creates a menacing tone by personifying the earth with the qualities of a living, powerful creature.
Step-by-step explanation:
The simile 'the earth still rose and fell like a great animal breathing' in the passage from Scott O'Dell's Island of the Blue Dolphins enhances the passage's meaning and tone by likening the movement of the earth to the rhythmic breathing of a large creature. This comparison evokes a sense of the earth being alive and somewhat unpredictable, which contributes to a menacing tone rather than a light-hearted or bitter one. It underscores the earth's power and the character's vulnerability in the face of natural forces, emphasizing the wild and possibly dangerous environment in which the characters find themselves.