Kino has to treat Juana more harshly as the novel goes on because the peace of his world is completely disrupted. He has to become more concerned about the safety of his family and is unable to enjoy the "Song of the Family" because the Pearl of the World has ruined all that.
Quietly he tracked her, and his brain was red with anger. She burst clear out of the brush line and stumbled over the little boulders toward the water, and then she heard him coming and she broke into a run. Her arm was up to throw when he leaped at her and caught her arm and wrenched the pearl from her. He struck her in the face with his clenched fist and she fell among the boulders, and he kicked her in the side.