Lisa's Date with Density a child from Josh Weinstein's school days who everyday would get onto the bus with a piece of toast, which had Vaseline on it. A majority of the story is a reference to the film "Rebel Without a Cause". Lisa remarks that Nelson is "like a riddle wrapped in an enigma wrapped in a vest", a reference to "a riddle wrapped in a mystery inside an enigma"; this was Winston Churchill's opinion of Russia at the outbreak of the World War II. In its original broadcast, "Lisa's Date with Density" finished 63rd in ratings for the week of December 9–15,
The Riddle of the Sphinx (Inside No. 9) the episode's close. Shearsmith identified "The Riddle of the Sphinx" as one of his two favourite episodes of the series, along with "The Devil of Christmas". For the writers, the episode was not comedic, and they expressed awareness of the differences between episodes of "Inside No. 9" like "The Riddle of the Sphinx" and the expectations of viewers for television comedies. The pair acknowledged the particular complexity of the plot, with Pemberton saying "If you missed two sentences in a row, you'd be like 'what?' Even I was thinking how are people following this? It's insane." Pemberton had long been