This episode shows one of those instances when "For He's a Jolly Good Fellow" is sung instead of "Happy Birthday To You". Until 2016 in the United States (and 2017 in the European Union) "Happy Birthday To You" was actually a licensed song that requires the payment of royalties if it is used in any media, while "For He's a Jolly Good Fellow" is still in the public domain.
Gilligan breaks the Fourth Wall in this episode & also addresses the audience at the end of the episode.
Mary Ann actually shows off her belly button in this episode which is a very rare instance within the series. In the same scene, Ginger's is covered by a jewel.