The title of the episode is drawn from the lines, "How sharper than a serpent's tooth it is / To have a thankless child!" The lines are spoken by Lear in William Shakespeare's "King Lear," act 1, scene 4, lines 288-289.
The set used for the Chancellors' apartment is the same set used for Peggy's apartment (see, e.g. the premiere episode for this season, Eagles Sometimes Can't Fly (1969) or the previous season's Last Rites for Miss Emma (1969)).
When Mannix and Peggy are reviewing the newspaper microfiche of the robbery the Time magazine on the bookshelf behind them is the November 1, 1968 issue featuring Mayor Lindsay on the cover.
Fourth use of the Herbert's Delicatessen street set.
The apartment that Cap and Gaines share has at least two posters for the Darlington 500 held on Labor Day Monday, September 2nd. The Southern 500 NASCAR race was traditionally held at Darlington on Labor Day Monday from 1950 through 1983, and has been held on Sunday (mostly over Labor Day) since. Prior to this episode, only three races were held on Monday September 2nd - in 1957, 1963 and 1968.