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) was able to include "MYSTERYGUEST", "KNOWITALL", "UNDERSLIP" and "NEUN". The episode's second nina was created accidentally and seen at the last minute; by introducing a middle name for Pemberton's character, the writers were able to make it a part of the plot. At least one of the clues used in the episode—Squires's improvised "I teach wild creature without hospital building", resulting in "ARCHITECTURE"—was not a good one. This was acknowledged by Squires in the episode, but was kept in as it reflected Squires's view of his own actions. Pemberton hoped that "The Riddle of the Sphinx" would work as a