It is alluded that Flaubert wrote The Flowers of Evil, a French book of poetry. In fact, the author was Charles Baudelaire; Flaubert is famous for Mme. Bovary, amongst other works.
The mother has a problem with her son reading French literature of the XIX (19th) century, namely the Flowers of Evil by Charles Baudelaire, whose work is erroneously attributed to Flaubert. Both authors' works are also erroneously referred to as pertaining to the Existentialist period. This is incorrect: French literature of the 19th century pertains to the period known as Romanticism (the authors known as The Romantics). The French Existentialist literary era pertains to the mid 20th century, which did not exist when Flaubert, Baudelaire and Rimbaud [at the end also erroneously attributed to the Existentialist period] wrote books in the 1800s. [Albert Camus and Jean-Paul Sartre are the most well-known authors of Existentialism, which had its peak in 1945.]
Friday drops a thick blue book on his desk at the end: the word Flaubert is written in felt pen on its spine, while the book title has evidently been erased. This episode attributes The Flowers of Evil book to the wrong author (it was written by Charles Baudelaire and not Gustave Flaubert, as the show purports) and the wrong literary period (Existentialism, instead of the correct Romanticism). This might explain why the title has been removed from the book. It is unclear why the show would (perhaps purposely) attribute this book title to the wrong author. Of course in the 1960s, when this show aired, there was no internet for viewers to look it up.