Visible crew/equipment: When Doug and Arthur are eating in the buffet restaurant, stage lights are seen reflecting in the cup. Also, each time the camera goes from angle to angle, the cup has moved from one side of the table to the other, sometimes have a saucer, sometimes not. (00:06:35 - 00:08:20)
Visible crew/equipment: When Carrie and Arthur pull into the driveway, the camera is reflected in the car. (00:18:15)
Visible crew/equipment: When Arthur is hinting it's his birthday soon, there is one shot where you can see the cupboards above the hatch into the kitchen. In this shot you can see a boom mic follow Arthur across the room. (00:02:30)
Continuity mistake: At the buffet, the cup that is on the table is either on or off a saucer depending on the shot. (00:06:55)
Continuity mistake: When Doug and Arthur sit down to eat, the cup that is on the table is either by Arthur or by Doug depending on the shot. (00:06:35)
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)
Visible crew/equipment: When Doug mentions about a mistake in the word jumble, look in the glass above him to see a boom mic reflection clear as day. (00:01:45)
Visible crew/equipment: When Arthur walks into the living room humming the Happy Birthday tune, as he bends down to pick up the magazine, a camera is visible on the right side of the screen. (00:02:30)
Visible crew/equipment: After Doug gets Arthur out of the house he takes him to a restaurant, and as they both take their seats, the two sets of double tape marks are visible on the carpet under the table. Then, when Doug stands up another small tape mark is visible at his feet. (00:06:30 - 00:08:00)
Continuity mistake: When Arthur's friend Mr. Glassman comes into the Heffernan house, a large tree can be seen on the front lawn, which we know from many other episodes there is not a large tree in front of the Heffernan house. (00:09:30)
Visible crew/equipment: When Doug is sitting in the living room and Carrie comes into the kitchen carrying groceries, a boom mic shadow is seen moving on the wall behind her. (00:04:10)
Continuity mistake: Doug and Carrie are fighting in the kitchen. Around the time that Carrie says, "I give you one thing and you screw it up," Carrie's handbag in the background is standing upright. The shot goes back to Doug. When it goes back to Carrie and she is leaving, she picks up her handbag which is now no longer upright. Her handbag also looks like it has been shifted.
Continuity mistake: When Doug is going into the living room after Carrie has gone in search of Arthur, his left hand is on the door. When he goes through the door, he is opening it with his right hand. (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.