In this passage from Walden, what analogy is Thoreau using?

Let us spend one day as deliberately as Nature, and not be thrown off the track by every nutshell and mosquito's wing that falls on the rails.

He is comparing life to a moving train

He is comparing nutshells to mosquito's wings

He is comparing nature to problems

He is comparing life to nutshells

Henry David Thoreau was an American essayist, poet, philosopher, abolitionist, naturalist, tax resister, development critic, surveyor, and historian, two of his greatest works are: "Resistance to Civil Government" (also known as "Civil Disobedience") and "The Mask of Anarchy". His ideals can be summarized by this statement: "the Government should not have more power than the bestowed by its citizens".

Henry David Thoreau was even imprisoned for refusing to pay taxes in protest for the Mexican-American War and the slavery.

In this passage from Walden, Thoreau the analogy is:

He is comparing life to a moving train

Here we have the evidence to support the analogy:

Let us spend one day as deliberately as Nature, and not be thrown off the track by every nutshell and mosquito's wing that falls on the rails.