When Endeavour is explaining to Thursday how he knows that Terence Black is the killer he describes the coat of arms Weiss was creating for Black.
He says: "It was unnamed, but it included various clues in the form of rebuses, heraldic jokes which would suggest it was meant for Terence Black.
The escutcheon is sable, the heraldic term for "black".
In the upper sinister quadrant is a pick-axe, or pick, while the lower dexter quadrant contains flowers of the genus Matthiola longipetela, also known as stocks."
But when we see the coat of arms the pick-axe is in the upper-left from our point-of-view which is the Dexter side - similarly the stock is bottom-right which is the Sinister side. Sides are named from point-of-view of the bearer of the shield - not the viewer.
At the time when it is supposed to take place no nurse was allowed to wear her uniform outside of the hospital (unless a District Nurse or a Midwife).
Young Morse's next-door neighbor, the nurse with whom he has a long-standing soft-spot is often seen wearing her uniform. In Morse she was played by a white actress.
The episode is set in the summer of 1966, with schools on holiday and the World Cup reaching its final stages. The double-bill of "The Reptile" and "Rasputin - The Mad Monk", which Morse and others see at an Oxford cinema, went on general release on March 7th of that year, and therefore would have been seen in a town as big as Oxford by Easter at the very latest.
Mr Fitzowen gives Morse and Thursday a slide show of official police photographs of murder victims in a crime scene from 1866. However, there's little evidence that forensic photography was used for this purpose at this time. Even infamous cases like the Jack the Ripper murders were not photographed (with the exception of the last murder) and they were committed 22 years later.
Stephen Fitzowen claims to have been recording supernatural phenomena with a portable tape recorder for over 40 years. Portable reel-to-reel tape recorders were not available until the late 1940s. This story is set in 1966. Correction: he said he has been making recordings but he didn't say how. There were other methods prior to reel-to-reel.
When Morse is investigating the disappearance of Bunty Glossop, he says "there aren't many girls who could offer an apt Lewis Carroll quote." Morse, a stickler for excellent grammar, would know that "quote" is a verb, not a noun. The correct word is "quotation". Not a goof: "quote" is also a noun whose definition is both "quotation" and "quotation mark."
As Morse falls through the floor the break is clean but in the next shot as the camera looks down at him the break is jagged.
Miss Danby tells Morse that the missing girl "clung to Miss Symes and I like a suckling child to its mother" - needless to say, a well-educated young woman of the 1960s, let alone a schoolteacher, would have known better than to perpetrate so obvious a grammatical howler and would have said "Miss Symes and me".