"Mais où sont les neiges d'antan?" ("But where are the snows of yesteryear?"), Violet's line, spoken in French, referring to her having known Lord Hepworth's father in her youth, is from the poem "Ballade des dames du temps jadis" by François Villon.
Daisy finds a Ouija board on the shelf downstairs. These boards came along after the American Civil War and were used by spiritualists to talk to the dead. The Ouija board was patented in the 1890's in the US. They were wildly popular after WWI. The one they're using is a generic talking board of Brit manufacture; on the money bag is the symbol of the English pound. Although science has proven these talking boards are really operated by the subconscious mind, the Catholic Church still has them outlawed for use.
Lord Hepworth, played by Nigel Havers, is named for Hepworth, Cecil, and his company, Hepworth Studios, where actress Ivy Close, grandmother of Downton Abbey (2010) producer Gareth Neame, got her start in the film industry.
In the first and second season characters make fun of Edith for her wanting to be with Anthony Strallan even though he is considerably older than her. However they don't say a word about Mary and Richard Carlyle who is also older than she is. They don't say the ages of Anthony and Richard, but in real life both men are older than Hugh Bonneville who plays Edith and Mary's father.
Mary mentions that her grandmother, Cora's mother, has houses in New York and Newport. Along with Cora knowing JJ Astor, son of the infamous Mrs. Astor, this adds to the idea that the Levinsons are a notable family of the Gilded Age and very likely to appear in later seasons of Julian Fellowes prequel series The Gilded Age.