"I'm sorry, Nina...I thought that I could tell you my true thoughts at first, since you're a mature adult and all. But after seeing how absolutely innocent you are, like an unblemished piece of white paper, I've changed my mind and don't want to say anything to you since I really don't want to stain your pure mind with my filth."
Kafka sighed like it couldn't be helped and looked at Nina with an apologetic look on his face for not keeping his end of the promise. He genuinely couldn't carry out what he said he would do, and he wasn't exaggerating in any way, as saying anything vulgar to Nina felt like talking dirty to a pure child, which he could never bear to do.