Thoreau's Journal - Listening

What is Thoreau talking about in the following diary passage?

He speaks of the wind and the noise of a toad. But he also reminds us of the magic that happens when we quiet the mind to observe what rises up and falls away:

"When I stand out of the wind, under the shelter of the hill beyond Clamshell, where there is not wind enough to make a noise on my person, I hear, or think that I hear, a very faint distant ring of toads, which, though I walk and walk all the afternoon, I never come nearer to." -- Henry David Thoreau, from his journal, April 5, 1860