When one of Fat Tony's goons has Homer in a mounted position, and tries to stab him with a knife, the knife changes from a single edged blade to a dual edged or dagger-like blade.
Mayor Quimby sits on the bench after Homer saves him, A few seconds later when people run out of the building he is not there. In the next shot he reappears.
When Quimby is dangling from the window, an external view shows that his head is clearly elevated above the top of the window, but the view from inside the same window shows his head well below that point.
The Lost in Space (1965) Robot warns Bart about the evil of Dr. Smith, by rephrasing its old tagline "Danger! Danger! Will Robinson!" as "Danger! Danger! Bart Simpson!" But Bart has never told his name to anyone from this delegation, so there's no obvious way for the Robot to know it.