As well as Joseph Merrick (The Elephant Man), Jasper Hammond's lecture slides in the opening credits show Ella Harper (The Camel Girl) and Myrtle Corbin (The Four-legged Woman).
The episode title and Jasper's later reference to seeing a solitary magpie both refer to a well known British nursery rhyme called "One For Sorrow" that relates to magpies. The rhyme was first documented around 1777 in John Brand's book "Observations on Popular Antiquities in Lincolnshire." The rhyme contains the following verse, relating to the significance of the number of magpies observed: "One for sorrow, two for mirth, three for a funeral and four for birth." The nursery rhyme evolved over many years to its current form, which also includes "One for sorrow, Two for joy, Three for a girl, Four for a boy".
The poem Hathaway reads to his father is "God's Grandeur" (1877) by Gerard Manley Hopkins.
Nicholas Jones--who appears as Hathaway's father Philip--was a co-star with John Thaw on "Kavanagh QC (1995)," which started broadcasting during the later years of "Inspector Morse (1987)."