Revealing mistake: When Bud is at the shoe store with Al, right after Bid says something about the woman with chicken wings, you see the flash from a camera.
Can't Dance, Don't Ask Me (aka Kelly's Dance) - S3-E13
Continuity mistake: During Kelly's dance, a nerdy girl grabs Bud and starts kissing him, but in the next shot, Bud is standing alone in the background. (00:20:30)
Can't Dance, Don't Ask Me (aka Kelly's Dance) - S3-E13
Continuity mistake: While Kelly is dancing with the guy at school, a nerd girl starts kissing on Bud and pushes him backwards. The very next second when the scene changes, Bud on the left side is back playing the record for the music without anyone around him.
The House That Peg Lost - S3-E16
Plot hole: Marcy and Steve live on the left-hand side of Al and Peg yet when they come home and see their house is gone Peg is looking out the window in the front door saying they're looking at the hole now they're looking over here.
Other mistake: Al, Peg, and the kids go to the beach. Steve and Marcy are sitting not too far away from them, yet they never interact with each other. They had to see each other they just act like they don't notice each other.
Continuity mistake: When Kelly is at the grill, right after being called a "dullard" by Bud, Kelly grabs Bud's wrist with her left hand. As we pan out on the exact same scene, her hand is nowhere near his wrist.
Factual error: Al uses ashes to cook food on the grill. You can't just throw ashes in a grill and light them! They wouldn't light at all. That's like trying to light cigarette ashes and expecting them to burn hot enough to cook food.
Dead Men Don't Do Aerobics - S4-E2
Other mistake: Jim Jupiter stays with Peg for a week. 6 days later he's shown heavier than he was before. You don't gain that much weight in 6 days.
Dead Men Don't Do Aerobics - S4-E2
Revealing mistake: When we see Jim Jupiter on his show after gaining weight, you can plainly tell he's wearing padding under his clothes to make him look fat.
Continuity mistake: Al takes the kids camping. When he leaves the house, his shirt is light blue. When he comes out from the bushes in the woods, it's dark blue with red stripes.
Plot hole: Al can't eat because his mouth is numb. So they go ahead and eat. Al can eat after the novocaine wears off and Peg can put leftovers in the fridge. They all act like Al can't eat for days and there won't be any food left.
He Ain't Much, But He's Mine - S4-E5
Plot hole: Marcy gets her hair done like Pegs. Everyone makes fun of her saying she looks ridiculous. All she has to do is wash it! Its obviously held up with hairspray but Marcy acts like there's nothing she can do about it.
Desperately Seeking Miss October - S4-E7
Revealing mistake: In the scene where Al and his Dad (both played by Ed O'Neill) are sitting on the couch side by side watch the lines of the cushion in the middle. Every time one of them moves you can see where the two separate shots are overlaid. (00:14:15)
Factual error: The sheriff does not come to your house and take your credit cards just because they are maxed out. The only time they would do that is if you stole someone else's card and were using it.
Visible crew/equipment: After Al fixes the roof and Peg reminds him to fix the TV antenna, when Al says he can do it, a shadow can be seen moving across the blue bucket on the table. (Probably a crew member or equipment.)
Factual error: Peg says she did the taxes and claimed 23 children. First of all, you can't. Max number of dependents is 2-3, and second you have to have birthdates and social security numbers for everyone. You can't just write whatever you want and send it to the IRS. And it's a joint return yet Peg says she didn't sign her name. You have to. So in reality, she would get in trouble too since she actually lied on the tax return.
Continuity mistake: A lady agrees to buy some of Peg's red hair. It shows the lady with two baggies with red hair in them, but at the end of the episode we see that they used Buck's hair, which is far from being red in color, or anything like human hair.
Deliberate mistake: When the family is trying to get money from Al at the start of the episode, he throws it on the ground making the rest of the family to dive on it and you can see Bud get it, then throw the bunch of money in the middle of Kelly, Peg and Bud so they can all get to it instead of taking it all. (00:02:10)
Continuity mistake: When Kelly blows up the car near the end, when they show the car before it explodes, you see someone walking on the right side behind the car. Half a second later the car explodes and now someone is walking by the building on the left side of the screen. There wasn't anyone there before.
You Gotta Know When to Fold 'Em (2) - S4-E17
Plot hole: Al hasn't got enough cash to pay for a pizza and Peggy overmaxes his credit cards. But somehow he manages to buy three flight tickets for Chicago-Las Vegas. Where'd the money come from? Also, when his card is declined, he calls the pizza shop back (they call him "no tip" Bundy), and somehow they know where Peggy maxed out the credit card. (00:05:15)
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.