Biting words can be delivered in such a way that they are not biting - they are instructive. Even thinking there's a meanness to it is implying a tone. Someone like Catherine who is trusting in Henry's complete goodness and sincerity would never take offense to anything he says, since she truly expects him to be instructive and kind to her, as he ever has been. And if he isn't, she would think it is because she deserves it! She is a completely trusting soul, and Henry relies on that sentiment as well as a smooth and a truly concerned delivery which masks all the art in his message, which Catherine will never be offended by. I know I would not react like Catherine does, but I do not have her artless and egoless nature. And I would be sarcastic back, I am sure! :)