Visible crew/equipment: When Doug says that Carrie is making progress with her room, a boom shadow can be seen moving along the door. (00:03:30)
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)
Visible crew/equipment: When Carrie and Doug head out to the garage the first time, a boom mic is reflected in the door's glass. (00:04:05)
Revealing mistake: When Doug tells Arthur his toast is done, there is no smoke, but as soon as he is finished speaking there is smoke coming from the toaster. (00:04:05)
Continuity mistake: After Doug has shot himself, the position of the staple gun on the bench keeps changing without anyone touching it. (00:06:40)
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)
Revealing mistake: Just as Arthur goes to look in Carrie bag, there is a wide shot and a cabinet can be seen by the door. In the glass of this cabinet's door, you can see a stage light reflected. (00:11:45)
Revealing mistake: When Arthur is looking in Carrie's bag, there is one shot with a blue kettle next to the bag. 10 stage lights can be seen reflected in the kettle. (00:11:50)
Continuity mistake: When Carrie confronts Arthur about looking in her bag, her bra strap is slightly hidden by her top. Camera cuts to a front view of Carrie then back to behind her. Now her bra strap has moved and is totally visible. Carrie never touched it during this time as we see her hands. (00:12:25)
Other mistake: When Doug is drawing a picture to explain to the nurse why he is there, a man purchases a beverage from the "Hot Drinks" machine behind Doug. The drink is ready unrealistically fast and the man immediately takes a sip from an obviously empty cup. Those machines produce notoriously hot beverages, so if the machine actually worked the man would have scalded himself.
Continuity mistake: When Doug has just shot himself and Carrie calls him at work, he looks back to Deacon before answering the phone. On the platform behind Deacon, a woman IPS employee appears instantly. Also, the IPS staff walking behind them do not match between shots.
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.