The yellow and black book you see is the distinctive cover of a
Cliffs Notes book that are amazingly popular in the states as 'study guides'. They basically tell you all the answers to questions that commonly occur on a whole range of classic texts studied in American high schools and colleges. It's fairly common for students not even to bother reading the actual text but just to read the cliffs notes summary and base their whole essay or whatever off that.
Anyway the joke is James doesn't really have insight into her heart. He has just been telling her the 'correct' things without understanding what they are or why they are important. The cut-off last line is "I was just supplementing..." which everyone says when they are caught by their teacher reading the cliffs notes, to try to pretend your reading it for additional ideas and not just stealing your whole essay from it's pages.