John Constantine says "Allons-y Alonzo", a reference to a the line said by the tenth doctor in Doctor Who. Russell Tovey (Ray Terrill) was the character Alonzo in the episode that the line is referencing.
The "ice pick" or "transorbital lobotomy" procedure that was going to be inflicted on Snart, was a common treatment for mental illness in the mid-twentieth century.
Mentions are made of Constantine's failure to save a girl named Astra. The failed exorcism is first mentioned in "Non Est Asylum (2014)", the premiere of Constantine (2014), and its haunting of John is a recurring theme throughout the series.
The empty room in the asylum that Ray tells the team to take Nora to, is room 237, a reference to the hotel room from the Stephen King novel and movie The Shining (1980).
The set used for the hospital scene in 1969 is the same set used in Supernatural season 1 episode 'Asylum' and season 2 episode 'In My Time of Dying'.