His neck stretched out a little--his ears laid back along the neck--his whole body settled gradually and continually down as his stride lengthened.

Whistling Dan was leaning forward so that his body would break less wind.

He laughed low and soft as the air whirred into his face, and now and then he spoke to his horse, no yell of encouragement, but a sound hardly louder than a whisper.

There was no longer a horse and rider--the two had become one creature--a centaur--the body of a horse and the mind of a man.
For a time the roan increased his advantage, but quickly Satan began to hold him even, and then gain.

First inch by inch; then at every stride the distance between them diminished.