It is through these subtle details that we learn something about Jay Gastby. Wolfsheim's cufflinks are made from human molars. That is a pretty disgusting thought because we can't help but wonder what kind of person would want them and what is he trying to say about himself by wearing them? Fitzgerald wants us to think about the gruesomeness of the cufflinks and think about how they must have been extracted -- probably under torture and then think about why he wears them -- as a sign to his friends and enemies that he is not afraid to send the message to not mess with him and his business. He is likely in the mafia, and that would explain how Gatsby came by such excess of wealth in such a short period of time. If he is willing to associate with people like Wolfsheim, then that is saying something rather unsavory about his character. Wolfsheim's comment about Gatsby is another piece of their relationship. Wolfsheim wants to run his illegal activities and not get caught. By working with someone like Gatsby that appears to be of fine breeding with his Oxford education and heroic war medals, and his 'above reproach' behvior, it makes their business less suspicious and keeps Wolfsheim 'above the law'. Gastby isn't a criminal by nature -- he is only doing what he has to do to get the money that he thinks will attrack the attention and the love of Daisy.