Tank Heaven - S6-E21
Visible crew/equipment: When Doug and Carrie close the door after saying bye to the first couple, you can see camera lights and a boom mic moving in and out reflected in the window behind them. (00:06:10)
Tank Heaven - S6-E21
Continuity mistake: In the scene where Danny has just taken the "nucleus" nacho chip, after Carrie walks in, the chip in Danny's hand keeps changing between shots, then disappears altogether almost instantly and his arms are folded when he begins his next line. (00:02:30 - 00:03:25)
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.