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
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 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.
Revealing mistake: While they are jousting, there is no one at all next to the stage in the wide shots. Every time they show the stage up close, there are 40-50 people. It changes back and forth the whole scene.
Every Bundy Has a Birthday - S7-E3
Revealing mistake: At the park when Al hits the rich man, he goes down like he was knocked out. Soon after, Seven punches the kid. In the background the rich man is actually sitting up on his side and he looks at Al and Seven, then as the camera pans towards him, he lies down on his side like he is passed out again.
Kelly Doesn't Live Here Anymore - S7-E8
Revealing mistake: You can plainly tell that Kelly is wearing a beehive wig at the diner when Peg comes and talks to her.
Revealing mistake: Kelly is making popcorn on the stove. It starts popping even though the heat isn't even on.
Revealing mistake: The burglar uses a crow bar to open the sliding glass door. You can plainly see him "pretending" he had to use it when it just opens easily. He didn't really pry it open.
Movie Show - S7-E21
Revealing mistake: When everyone is standing at the snack bar eating all the food you can plainly see all the candy boxes are empty and already open even though they were sealed when the cashier put them on the counter.
Movie Show - S7-E21
Revealing mistake: When Kelly is eating the boxes of candy you can plainly see they are empty, but she's chewing anyway.
Revealing mistake: When Kelly is at the house of the crazy guy who made the couch, when they drink the cappuccino and he throws the cup, it's clear that the cups are just props as the drink stays in when it falls towards the camera.
Revealing mistake: When the chain is cut from Al's wrist, you can see and hear that it's plastic not metal. (00:02:28)
Revealing mistake: Kelly lost all her hair as a side effect from pimple potion. You can see the lines on her forehead that show she's wearing a flesh piece covering her hair to make her look bald. The color is lighter than her face. (00:18:42)
Revealing mistake: When Kelly goes for her commercial, you can see that there is a stocking head cover to make her appear bald.
Guess Who's Coming to Breakfast, Lunch and Dinner - S10-E1
Revealing mistake: Near the beginning when Al is looking for his magazines under Bud's bed, a large shadow of someone crosses over him showing someone in production crossed in front of the lighting.
Revealing mistake: When they blow up the scoreboard at first in slow motion, the entire scoreboard is blown up and destroyed. The next shot only a small portion at the top and middle is destroyed, not the entire thing.
I Can't Believe It's Butter - S10-E13
Revealing mistake: When Griff drinks the gravy right before calling "Butter", his glass is empty.
The Hood, the Bud and the Kelly (2) - S10-E15
Revealing mistake: Whenever Al or Jefferson falls off the roof you can plainly see it's a dummy wearing their outfits.
Breaking up is Easy to Do (2) - S11-E15
Revealing mistake: When Al falls on the bed with the shoe and puts the hole in the water bed, the shoe doesn't hit the bed anywhere near where the water starts to shoot out from.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.