Continuity: When Bart's army is attacking Nelson, there are a lot more kids attacking Nelson then there were training with Bart.

Continuity: At the start when the bully takes the cupcakes, you can see that after he has started eating them there are 4 left in the box. Just before he shuts the lid to drop it, you can just see the tops of 6 cupcakes.

Factual error: When Bart declares war on Nelson, Herman uses the declaration from the Franco-Prussian war and puts "Bart" in place of "Otto Von Bismarck". The thing is, Bismarck didn't declare the Franco-Prussian War, Napoleon III of France did. A small error, maybe, but something that a war buff like Herman should know.

Deliberate "mistake": When Grandpa Simpson is typewriting a letter in his room, the words he's spelling out loud don't match his fingers hitting the keys.

Continuity: When Bart enters the tree house after being beaten up, he puts his hat on a peg behind him. In some later shots at an angle you can just see the hat behind him. In the shots from directly in front of Bart, the hat is not on the peg.

Continuity: When Bart is training up his army, the colours of the kid's tops keep changing between shots.