It is the trait of a savage.

That truculent knob and that truculent bull-neck correlated themselves most horribly in my mind.

And again, with a shiver, I had the haunting flash of a vision of him, out of the tail of my eye, standing rigid and gaping between the two cars, while my rugged old Marigold, in a businesslike, old-soldier sort of way, without thought of danger or death, was swaying at the head of the runaway horse.
Presently he turned, and his brows were set above unfathomable hard eyes.

The short-cropped moustache could not hide the curious twitch of the lips which I had seen once before.

It was obvious that these few minutes of silence had been spent in deep thought and had resulted in a decision.