Wordplay. Mario Puzo is the author of the novel that the famous film The Godfather is adapted from. A famous line from the movie involves one character saying that they will intimidate another into following their orders by "making him an offer he can't refuse". The pun is on the similarity in sound between "offer" and "author"; the students cannot refuse to read Puzo's works because he is required reading for the class.
When she made Mario Puzo ' s books required reading for her class , she made him an author they couldn ' t refuse .