"Asking a critic to name his favorite book is like asking a butcher to name his favorite pig"

John McCarthy's quote is a humorous method of saying that it is tough for a critic to choose a preferred book, simply as it would be difficult for a butcher to select a favorite pig. The quote indicates that a critic is so knowledgeable about books that it is difficult for them to pick a favorite, just as a butcher is so knowledgeable about pigs that it is difficult for them to select a preferred. The quote also indicates that a critic is so vital of books that they can not select a favorite, just as a butcher is so knowledgeable about the anatomy of pigs that they can not select a preferred. The quote is a humorous method of stating that it is challenging for a critic to select a preferred book, just as it is tough for a butcher to select a favorite pig.