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: When Doug and Deacon are talking about Doug wearing a disguise to the concession stand, There are two people on the loading bay holding a parcel. Camera cuts and this parcel is no longer in their hands. (00:13:00)
Continuity mistake: Deacon says "How do we know cutie-pie isn't cutie-guy?" then crosses his arms. In the next shot his arms are immediately uncrossed and on his hips when Doug replies. (00:06:00)
Taste Buds - S5-E24
Other mistake: When Doug sits down to eat and Arthur touches his food, Doug says, "That's what my sandwich was missing, a finger with a loose bandaid on it," and pushes Arthur's hand away. When he does this you can see Arthur isn't wearing any bandaids on his hands. (00:00:05 - 00:01:00)
No Retreat - S4-E5
Other mistake: In the opening scene when Doug is cooking hotdogs for his friends, the smoke coming from the BBQ is very fake. (00:00:20)
Other mistake: At the end when Doug takes the bandages off Carrie's face, the bandages come off far too easily as if they weren't really attached in the first place.
Revealing mistake: When Doug stops to tie his shoe outside the car dealership and Carrie walks up to grab him, you can see the fake back-drop sway with her motion. (00:08:35)
Dog Shelter - S5-E23
Visible crew/equipment: When Doug finds out that Rocky is in fact Rocky 4, a boom mic is reflected in the window. (00:10:20)
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.