Use the back of the book and put it in your own words.
They logged thousands of miles and battled fierce snowstorms
IMPROVISATION
Musical improvisation, also called musical extemporization, is the invention of music “in the moment”. Improvisation enables the performer to communicate and interact with other musicians promptly, spontaneously, and naturally. Musical harmony, melody, rhythm or any component is immediately created automatically.
Kafka uses the definite article "the" because it was not a simple metamorphosis. It was a specific changed that happened to the main character. Although it was not possible to happen in the real world, transforming into a giant moth represents the ultimate change that can happen to anyone.