In Aziraphale's shop, laying on a pile of books, can be found a copy of the Terry Pratchett Discworld novel 'Feet of Clay'.
A "shake" is an informal unit of time equal to 10 nanoseconds. It is used in nuclear physics to conveniently express the timing of various events in a nuclear reaction, especially neutron reactions. The typical time required for one step in the chain reaction is of the order of one shake, and the chain reaction in a nuclear weapon is typically complete by 50 to 100 shakes. Like many nuclear units, it came to be adopted during the Manhattan Project of World War II. It was derived from the expression "two shakes of a lamb's tail", which indicates a very short time interval.
When Newt is listening to James Naughtie interview an Electricity Board spokesman about the missing nuclear material from the power station, the spokesman is voiced by Paul Kaye. Kaye played Terry Pratchett in the documentary Terry Pratchett: Back in Black (2017), and Pratchett was once a press officer for the electricity industry. The voice Kaye uses for his role as the spokesman in this episode is his rendition of Terry's voice in the documentary, meaning that Pratchett can be heard in this series.
"When robins blue chariot inverted be..." While the car is painted almost Robin's Egg Blue, it is also a Reliant Robin. The three wheeled Robin is infamously prone to rollover but at less than 970 pounds is easy to roll back up.
Crowley's license plate reads "niatruc". That's "curtain" backwards.
Neil Gaiman: Appears in the movie theater when Hastur contacts Crowley. Gaiman is asleep a few rows ahead of Crowley.