He turned and examined the gulch, but it was narrow and grassy and had no possible place of concealment, and save himself and his own horse it was empty.

And it was not his own horse that whinnied--he was sure of that.

Also, he was sure that he had-not dreamed it.

A horse had called insistently.

Andy knew horses too well not to know that there was anxiety and rebellion in that call.
He waited a minute, his heart beating heavily.