Wakko opens a door on the boat and the Marx. Bros fall out of it, in reference to the scene from this film. Dot then says "They had to do the Night at the Opera bit"
Part of the lyrics to the Rita & Runt opening is "Like Abbott and Costello..." and when these words are sung we see Rita & Runt dressed up in baseball gear in reference to the famous "Who's on first" bit from this movie.