Not for a long, long while had Casey been cautious in his behavior, and the necessity galled him.

If the hidden marksman had missed that last burro, Casey would probably have taken a longer chance.

But to date, every bullet had gone straight to its destination; which was enough to make any man think twice.
Once during the forenoon, while Casey was standing against the rim-rock staring glumly down upon the camp, Barney's hat, perched on a pick handle, lifted its crown above the edge of his hiding place; an old, old trick Barney was playing to see if the rifle were still there and working.

The rifle worked very well indeed, for Barney was presently flattened into his retreat, swearing and poking his finger through a round hole in his hat.
Casey seized the opportunity created by the diversion and scurried like a lizard across a bare, gravelly slide that had been bothering him for half an hour.

By mid-afternoon he reached a crevice that looked promising enough when he craned up it, but which nearly broke his neck when he had climbed halfway up.