A hundred times when he was about to pull trigger he discovered his error.

Yet voices came from a distance, and steps and crackings in the willows, and other sounds real enough.

But Duane could not distinguish the real from the false.
There were times when the wind which had arisen sent a hot, pattering breath down the willow aisles, and Duane heard it as an approaching army.
This straining of Duane's faculties brought on a reaction which in itself was a respite.

He saw the sun darkened by thick slow spreading clouds.

A storm appeared to be coming.