The "Mapplethorpe" book of nudes which Homer inadvertently picks up is a reference to the work of Robert Mapplethorpe, a photographer whose work caused controversy due to its focus on the underground bondage and sadomasochistic BDSM scene of late 1960s and early 1970s New York City.
The word "Pneumonoultramicroscopicsilicovolcanoconiosis" which Grandpa uses in asking why Marge doesn't look well, is reputed to be the longest word in the English language; it is synonymous with the shorter word "pneumoconiosis" and refers to the lung disease also known as miner's lung.
Dan Castellaneta provides the voices for both Homer and Grampa. Castellaneta therefore had to talk to himself when he recorded the voices of the two characters in their interactions for this episode. Castellaneta says that it is hard for him to do Grampa's voice for an extended period of time because it is "wheezy and airy".
Homer is shown shaving off his stubble, which grows back moments later. This gag was also done in Some Enchanted Evening (1990), where Homer has a clean shaven look for precisely seven seconds, then his stubble regrows.
Milhouse's "we're through the looking glass here people". Is a quote from the 1991' movie JFK.