Revealing mistake: When Carrie phones Doug at IPS, Doug goes to press the button on the phone for the correct line, but doesn't press any and continues to talk to Carrie. (00:07:40)
Two Thirty - S4-E24
Plot hole: In this episode Arthur scams Deacon and several other parents for phony piano lessons because he doesn't actually know how to play the piano. However, earlier in the series (Art House episode, S1 - E24) we learn that Arthur can play the piano when he temporarily moves out and after his house warming party Doug says to Carrie, "Who knew Arthur could play the piano like that?"
Continuity mistake: When Doug, Carrie, Deacon and Kelly are looking at the damage caused by the accident, the same kid in the black and red hat checking his watch walks by twice. (00:05:10)
Other mistake: Spence eats some peanut M&M's despite being allergic to peanuts. (00:01:40)
Suggested correction: This episode was very early in the series, before knowing any history of the characters. Spence's peanut allergy came up in much later episodes. It is possible that he developed the allergy later.
It was stated that he had the allergy as a child.
Revealing mistake: When Deacon tries the doors on the van, the wall moves, revealing it's not a van but a set. (00:08:30)
Continuity mistake: In this flashback episode, when Doug is shaving his mustache and talking to Deacon by his locker at IPS, Danny Heffernan's name can be seen on a locker. At this time, Danny was not working at IPS.
Frozen Pop - S2-E15
Visible crew/equipment: At the very beginning, when Carrie walks in, a boom mic is visible above her. It then quickly moves out of shot. (00:00:05)
Head First - S1-E6
Continuity mistake: During the poker game, Arthur teases Spence because he's a virgin, which is mentioned later when Doug tells Cariie, "He teased him about the virgin thing." But in one of the later episodes, it is mentioned that Spence had an affair and had sex with his Home Economics teacher when he was very young and had long hair.
Suggested correction: Spence did have sex with the teacher, but the episode with the teasing at the poker game, Arthur and the guys don't know about her yet. Therefore, to their knowledge, Spence is a virgin, and for some reason, he decides not to defend himself with the teacher story.
The episode with them playing cards wasn't the only season 1 episode where Spence's virginity had come up. In season 1, episode 12, Carrie fixes Spence up with a coworker. When Richie and Doug tease him that they've already been together a month without sex they say: "Do you believe this guy?" "A month, huh?" Spence replies: "Yes a month! A month is not that long not to have had sex." To which Doug says: "Yeah, but if you add in the other 31 years, I'd think you'd be a little antsy." Also a little later in the conversation, when Doug tries to convince Spence that he and the girl have sex in his garage: "I'm just saying, if you wait too long, this opportunity could go bye-bye. Then it could be, hey, another 31 years before this opportunity comes again. It's pretty tough losing your virginity when you're 62." So Spence later already having lost his virginity in high school is a continuity error that they just overlooked and alas instances like these become apparent pretty often when you rewatch the show (like Carrie becoming an only Child, Arthur being said to be a great piano player in a season 1 episode while he can't play a single tune in a later season etc., etc).
Suggested correction: Spence was embarrassed about sleeping with the Home Ec. Teacher - which is why, in the high school reunion episode, he claims that he actually slept with his Spanish teacher. He also never called the Home Ec. Teacher after their "fling." Apparently he prefers to let the guys think he is a virgin.
Continuity mistake: When Doug sits down to read his book, he has his book on his tray. This then disappears as the shot changes. (00:11:20)
Continuity mistake: In the scene where Arthur is on the phone with PBS to complain about getting a "Civil War Series" box set, the actual set of tapes changes drastically. When it's on the table and when Carrie brings it over to the counter its a pretty large, has an American flag motif, and says "Civil War" across the top. When it cuts back to it sitting on the counter its a much smaller box with a plain design and says "The Great War" along the bottom. It's obviously a different set, not just the camera angle. (00:14:40)
Revealing mistake: In the final scene, Carrie starts to kiss Doug and pushes him onto the bed. The camera angle switches from what would be outside the window to beside the bed. The scene was done in one take from 3 camera angles. As the camera pans left you can see the center window is completely open because they had just pulled the camera out of it and didn't get it closed yet, and you can watch the window be closed by an invisible hand from underneath. (00:28:00)
Visible crew/equipment: When Doug is working at Cooper's, and goes to get the ladies beer nuts, the camera pans to the left, and a 2nd camera (which is used on the following shot of Doug) is visible on the left side of the screen.
Soft Touch - S2-E22
Continuity mistake: At the beginning, when Carrie is trying to park the car she's wearing a 3/4 sleeve blue top in the closeups, but in the overhead shot of the car for the last attempt when Carrie says that she's cutting it, the driver is not wearing that blue top, the driver is wearing a plaid shirt. (00:01:00)
Other mistake: In outside shots the front door is on the extreme right. Shots from inside the house show the living room on the left and the door in a central position.
Mammary Lane - S5-E5
Continuity mistake: At the beginning of the episode, the establishing shot shows a bowling alley with a sign that reads Mar Lin Do Lanes. A few minutes later, Doug welcomes Denise on behalf of the family at Bowl-O-Rama. (00:04:10)
Character mistake: In the opening scene, Doug call Carrie "Kel" which is Deacon's wife. He calls her that when he's saying they should just get a new grill.
Continuity mistake: When Doug and Carrie are in the living room talking about Doug not going out with Kelly again, he has the phone in his hand, gets upset and throws the phone down. Then Carrie is going to call Kelly for Doug, and when she goes to pick up the phone, it's placed perfectly back on the hook when it should be hanging near the floor from the way Doug threw it.
Visible crew/equipment: Near the beginning when Doug comes into the kitchen and smashes the cake with the watermelon, you can see a stage light reflecting in the door window 3 times as it swings open. (00:00:10)
Queasy Rider - S2-E1
Other mistake: Arthur gives his CV to Doug at the start. You can see it's typed but both Doug and Arthur talk about it being in magic marker. (00:00:30)