In the scene where Grampa Simpson crashes his car into the Aquarium tank, the water level in the tank begins to fall before Grampa's car hits the tank.
When Homer is wearing his XFL t-shirt the logo starts out as a black X with red writing on top, then changes to a red X with black writing later in the scene.
During the race, when one of Abe's friends reaches into the opposing car with a shoe on a stick, one of the men in that car cries out in Spanish, "Ay! Zapato del diablo!" This is translated as "Oh no! A shoe on a stick!" The correct translation is "Ow! Shoe of the Devil!" (This could be an intentional goof for humorous purposes.)