Continuity mistake: When everyone discovers Milhouse has eaten the food, Milhouse then says "You wouldn't dare hurt me. You forget, I have the glasses." After this line, Nelson takes off Milhouse's glasses. At this point, a rip is visible on the left side of Nelson's shirt. Milhouse then walks backwards and Nelson is seen re-entering the shot from behind Milhouse. Only now, the rip in Nelson's shirt is now suddenly on the right side of his shirt.
Other mistake: When Marge takes Homer back inside, his car is seen blocking the traffic. But at least one side of the traffic is driving on the wrong side of the road. The drivers behind Homer's car are on the right side of the road. And the drivers behind Homer's car from the opposite direction are driving on the left side but facing the drivers behind Homer's car on the other side. Either way, one half of the traffic are driving on the wrong side of the road.
Continuity mistake: Mr. Burns attempts to plan revenge on Springfield by placing the town in a dome. However when Lenny tells Burns it has already been done, Mr. Burns tells the helicopters to stop placing the dome. In this shot, both Burns' helicopter and the helicopters placing the dome are the same height off the ground. But in the following shot, the helicopters are now 50 feet above Burns' helicopter.