His master, free of egoism and prejudice, had placed him on a plane of intimate equality, and Peter struggled each day to live up a little more to the responsibility of this intimacy and confidence.

Instinct, together with human training, taught him woodcraft until in many ways he was more clever than his master.

And along with this Jolly Roger slowly but surely impressed upon him the difference between wanton slaughter and necessary killing.
"Everything that's got a breath of life must kill--up to a certain point," Jolly Roger explained to him, repeating the lesson over and over.

"And that isn't wrong, Peter.

The sin is in killing when you don't have to.