Z loves books. Yes, he loves to read, but that's not all I mean. He actually loves books, in an almost physical way. He pores over them and notes all sorts of little details: like the stuff about Library of Congress, whether it has a dust-jacket, how the contents are organized, whether chapters always start on a new page, how the pages are numbered.
He sometimes says that he's considering being an author when he grows up (because "creative writing" is his favorite subject in school). He will sometimes sit for hours at the computer creating "books". If one looks closely, though, an adult would conclude that his real career is going to be as a typesetter, printer, page-designer, editor, or publisher.
He does not just pore over his own books. He loves poring over mine too. He will take any book I'm reading and study it. He doesn't read it, but he'll study various aspects of these "big people's" (i.e. more real) books. Sometimes, he'll remember some crazy detail like: "Dad, wait, let me check" (runs away and comes back with an investment book I was reading four months ago), "Yes, I thought I remembered that. See, this book also has a chapter called 'Mister Market'".
Yesterday, he told me that one of my books was completely superfluous. "You don't need this book", he said, "because everything in it is in other books you have". Turns out that he had just gone through my "Ayn Rand Sampler" and cross-checked that all the essays were from books that I already own!