Nathaniel (Boy At The Cabin) Not Talking.

I don't really understand why the jerk (jerk because he stole Gideon's money) wouldn't ever speak, when Gideon first got there, or anytime, when Gideon asked him "You don't talk much do you?" then he just shook his head no, but then he only spoke when he figured he had too to save his sister from being raped or worse. He had very perfect speech when he did talk, so why refuse to talk except for a situation like that.