The final joke of this episode has Archie push Mike's face into the cake and Mike (being Mike) eating the frosting instead of wiping it off. But as the camera angle changes you can see Rob Reiner spit the blob of icing back into his hand just as the shot fades out.
After thinking of the plan to rent Mike and Gloria the house next to Archie, George Jefferson (Sherman Hemsley), says that he'll make Mike "an offer he can't refuse." This is a reference to the 1972 film, The Godfather.