When Myron is making insult jokes about Garfield he compares him to John, Paul, George, and Ringo. This is a reference to The Beatles.
Floyd complains about Penelope adding "or whatever her name is." This might be a tongue-in-cheek reference to the fact that Garfield's girlfriend in the comic strip is Arlene, not Penelope.
Unusually for the animal characters in this series, Myron the Mouse's mouth moves when he speaks.
Garfield's birthday is June 19th.