The company Monsarno is a reference to the real-life company. Monsanto
This episode marks the death of Edna Krapappel, because her voice actor Marcia Wallace passed away on October 25, 2013.
Next to a picture of Edna in the final scene of the episode is a picture of Maude Flanders, Ned's first dead wife. Ned's black armband confirms that Edna was killed off in an unknown fashion. In the episode, Ned says that Edna signed him and herself up for tango lessons.
The license plate on Marge's car reads "SABF07", which is the production number of this episode.
The name of Willie's mop is Ethel.
As of this episode both of Ned's wives are now deceased.
Pun license plates that Sideshow Bob was printing: