Visible crew/equipment: When Kel gets up to get more water you can see one of the cameras.
Bowling255
The Cold War - S1-E8
Revealing mistake: Cold War: The drill hole Kenan makes at the start is larger than the drill bit.
Ssiscool Doing Things The Hemingway - S1-E3
Revealing mistake: Kel takes the VCR player without unplugging it but Roger was watching a video seconds before.
Ssiscool Doing Things The Hemingway - S1-E3
Revealing mistake: The clouds are very obviously a set-drop when on the top of the CS tower.
Ssiscool Continuity mistake: In the episode when the president comes into Rigby's, near the start Kenan fixes the slush-o machine, but it doesn't work, and slush-o sprays all over Chris. Afterwards, one of the slush cups on the counter falls over. After that, the cup keeps on vanishing then reappearing.
Hamster Visible crew/equipment: When Roger is leaving you can see outside the door that the background is a painting.
Ssiscool Continuity mistake: Mo Sweater Blues: For the amount of water Kel splashes on Kenan the wet patch is way to big.
Ssiscool 
Answer: So that didn't feel he was being watched and judged by her.
Ssiscool