You Better Shop Around (2) - S5-E22
Revealing mistake: Marcy is stacking cartons of eggs in her arms. She turns around and a carton falls on the floor making a busted egg sound although the cartons are obviously empty.
You Better Shop Around (2) - S5-E22
Revealing mistake: When Jefferson starts to shove the 'regulation Foodies cart,' it's very obvious that the actor makes the shaking movements of the cart by himself. (00:08:05)
You Better Shop Around (2) - S5-E22
Plot hole: The supermarket director orders the photographer to take a photo of Al's special shopping cart. Then he turns around a little towards the cart. When the camera flashes, his right shoulder has to be in the whole left side of that picture. (00:07:50)
You Better Shop Around (2) - S5-E22
Revealing mistake: When Al 'bowls' Jefferson out of the way you can see the stuntman jump high and fall back into some kind of holding wire. It's an annoyingly bad stunt. (00:19:45)
You Better Shop Around (2) - S5-E22
Continuity mistake: The manager gives Jefferson a "wobbly" cart to use, but for the rest of the episode it's a normal, fast moving cart.
You Better Shop Around (2) - S5-E22
Continuity mistake: When Jefferson and Marcy are getting ready to take off during the supermarket race, Al sprays the floor with oil causing them to slip. Being that it is fresh oil, their clothes should have oil stains. But in the next scene, Jefferson and Marcy are perfectly clean.
You Better Shop Around (2) - S5-E22
Revealing mistake: When Marcy is stacking the cartons of eggs in her arms, you can plainly see that they are empty cartons.
You Better Shop Around (2) - S5-E22
Revealing mistake: Watch Jefferson and Marcy's feet at the end. They start to trip before the turkey even hits their feet.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.