Thunder rolled from under his hoofs.

And he broke out of that clattering roar into his fleet stride, where his hoof-beats were swift, regular, rhythmic.
Lucy rode him with teeth and fists clenched, bending low.

After all, she thought, it was no trick to ride him.

In that gait he was dangerous, for a fall meant death; but he ran so smoothly that riding him was easy and certainly glorious.

He went so fast that the wind blinded her.