Deliberate mistake: When Arthur enters the living room playing the harmonica, it is obvious he is not actually playing it. (01:23:10)
Revealing mistake: When the lights go out at the end of the episode, there is a reflection from a stage light very visible. (00:20:30)
Party Favor - S2-E13
Continuity mistake: When Doug is reading his speech to Arthur, Arthur's legs are crossed or uncrossed depending on the angle. (00:09:30)
Strike Out - S3-E7
Continuity mistake: When Arthur sits down for his meal, there is a bottle on the table. The lid is either on or off depending on the shot. (00:03:30)
Strike One - S3-E5
Visible crew/equipment: When Spence's taxi pulls away, a crew member, light screen and stage light can be seen reflected on the window of the taxi. (00:18:10)
Continuity mistake: When Carrie asks Arthur how a legless dummy will protect her on the subway, her arms are either on the table or off, depending on the shot. (00:10:30)
Soft Touch - S2-E22
Continuity mistake: When Doug is telling Arthur about the filters, there is a leaflet on the table. Between camera cuts, this leaflet is constantly changing position. (00:13:25)
Visible crew/equipment: When Doug walks out of Carrie's room, a boom shadow can be seen just outside the room on the wall. (00:03:35)
Queasy Rider - S2-E1
Continuity mistake: When Carrie says to Doug that he can't have a bike, her hand are behind her back. Camera cuts and now her bag is on her shoulder and her hands are on her bag. (00:03:00)
Queasy Rider - S2-E1
Continuity mistake: When Arthur gets the iron, he has it down by his side. Camera cuts and now it's up in front of his chest. (00:06:30)
Queasy Rider - S2-E1
Continuity mistake: When Doug and Carrie are arguing about the smoking for the first time, the cigarette has burnt down nearly half the length in a few seconds. Cigarettes don't burn that fast. (00:12:30)
Queasy Rider - S2-E1
Revealing mistake: Doug falls off the bike at one point and shouts that he has had enough. He opens the door and if you look carefully a stage light and boom mic are reflected in the glass. Slo-mo may help but is not essential for spotting the mistake. (00:15:25)
Continuity mistake: The Heffernans' house is one of a row of identical brick houses. However from inside the Heffernans' living room, you can see out the side windows that the neighbour's house is beige with horizontal paneling.
Continuity mistake: At the start, when Carrie is talking to Arthur about being inseparable she has her jacket over her arm. Camera cuts and now she is putting it on instantly. (00:00:10)
Continuity mistake: When Carrie takes a drink from her cup of tea she is holding her cup with 1 hand in one shot and 2 in a second shot. (00:14:30)
Queasy Rider - S2-E1
Continuity mistake: As Doug is telling Carrie he hates the bike, his beer and crisps vanish instantly from the sofa. (00:19:20)
Hi Def-Jam - S3-E13
Visible crew/equipment: When Mr. Purzan finds out that Stephanie doesn't want to date him and runs off like a little nancy-boy, we see his reflection pass through the picture in the hall. A moment later we can see the reflection of two people pass in the opposite direction but no one walks back into the room. (00:20:30)
Strike Out - S3-E7
Continuity mistake: After Doug says "Let's hit the streets", Doug, Arthur, Deacon and Kirby go on a mini crime-spree. During this montage each characters outfit completely changes several times. They are also dressed very lightly for late October/early November in New York. (00:13:00 - 00:14:00)
Answer: Sara hasn't been mentioned in later episodes, and it suggested in later episodes that she never existed, and that Carrie is an only child. Kevin James stated that the producers couldn't think of an good plots to use with Sara, so they left her out.