This is the first and only appearance of Doris Singleton as Harry's competent and efficient secretary Miss Singleton. Originally intended to be a series regular, the character was dropped as it was decided to show more of Lucy's family life with the kids rather than her job.
The title refers to the mod or MODernist subculture that originated in London, England in the late 1950s and peaked in the early to mid 1960s that was typified by fashion, pop music and British beat music.
Guest star Nancy Roth (Laurie) starred in Yours, Mine and Ours with Lucy, playing her step-daughter. Nancy Howard (Laurie's mom) was also in the 1968 film, playing the kids aunt.
Doris Singleton portrayed a character in this episode with the same first and last name as her. The real Doris Singleton played a reoccurring character named Carolyn Appleby (originally named Lillian Appleby) who was Lucy Ricardo's frenemy/nemesis.