While Don Adams is typing, he types the wrong letter and exclaims "Missed it by that much!" which was a catchphrase used by his character in his 1960's series "Get Smart!"
Gavin MacLeod and John Amos previously worked together on "The Mary Tyler Moore Show" (1970).
The title for the segment "The Zinging Valentine" is a play on a singing telegram/singing Valentine, wherein a messenger delivers a telegram/greeting via song.
A bit unusual compared to other episodes in that characters from all three separate stories interact with each other rather than remaining discrete from each other.