When Barney picks up Fred to go to work in the morning, the bird horn on his dashboard comes and goes.
When they write it, Wilma and Betty call the recipe the "Upside Down Flint-Rubble Bubble Cake." Later on, Barney, Betty and the announcer call it the "Upside Down Flint-Rubble Double Bubble Cake."
When Barney tells Fred to stop his outburst, Fred looks at him and asks him why. As Barney tells him off screen that he just "flipped his wig", Fred's lipstick disappears for a brief second before reappearing.
Fred apparently doesn't have a key to his own house.