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 crossword featured in "The Riddle of the Sphinx" was set by Pemberton, and was published in "The Guardian" on the day the episode aired, credited to "Sphinx". This crossword contains multiple ninas—hidden messages or words. Along with many of the crossword's answers, one nina is integral to the episode's plot. A second was introduced accidentally, and then incorporated into the episode. A third nina is an "Inside No. 9" in-joke. Influences for "The Riddle of the Sphinx", which emphasises gothicism over comedy, include Anthony Shaffer's 1970 play "Sleuth", the work of Anton Chekhov, and the 1989 film "The Cook,