Think meta. Don't think of people writing in a book. Think of controlling the person who's writing the book. Don't think of moving a person's arm but compelling the actual person to move that arm, all the while the person thinks he/she did it of his own volition. Mental suggestion, persuasion, subtle cues, etc. That's the true power of Descartes' Evil Demon. You don't know he exists because he's outside your context, yet he can alter your thoughts to make you do what he wants, all the while making you think it was our thoughts to begin with.