Though he did not realize the change in himself, six months of close companionship with the Little Woman had changed Casey Ryan considerably.

Time was when even his soft-heartedness would not have impelled him to patient scheming that he might help an old woman whose sole claim upon his sympathy consisted of four rock walls and a look of calm despair in her eyes.

Now, Casey was thinking and planning for the old woman more than for himself.
Wherefore, Casey chose the time when he was "putting in an upper" (which is miner's parlance for drilling a hole in the upper face of the tunnel).

He gritted his teeth when he swung back the single-jack and landed a glancing blow on the knuckles of his left hand instead of the drill end.

No man save Casey Ryan or a surgeon could have told positively whether the metacarpal bones were broken or whether the hand was merely skinned and bruised.
Joe came up, regarded the bleeding hand sourly, led Casey out to the dugout and bandaged the hand for him.