"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 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.
When Robert hears Sybil is pregnant, he states she has 'crossed the Rubicon'. The idiom "Crossing the Rubicon" means to pass a point of no return, and refers to Julius Caesar's army's crossing of the Rubicon River in Italy in 49 BC, which was considered an act of insurrection and treason. There was no turning back for Sybil now, Robert is saying.