Continuity mistake: Ms. Krabapple takes the cellular devices from the children in her class and puts them in a Laramie Cigarette box. She dumps the box into a desk drawer filled with frogs. A few seconds later there is a shot of the class from her point of view with all of their cellular devices on their desks.
Factual error: In the scene where Lisa's great great grandmother, and the slave Virgil escape to Canada, they enter Canada across a suspension bridge, which has, on the Canadian side, the Canadian Maple Leaf flag. In 1860, Canada was not yet even a country, and the flag was the Union Jack and the Canadian Ensign. The Maple Leaf was not adopted as the Canadian flag until February 15, 1965.
Continuity mistake: Season 20, episode 16, "Eeny Teeny Maya Mo." In the scene where Moe is cleaning his window inside the bar, take notice that the size of the spot he cleans on the inside of the bar is small. But when the shot changes to the outside, with Moe and the others looking out from the inside, the clean spot is larger.
Continuity mistake: At the end of "B.I.: Bartificial Intelligence," Homer climbs onto the ceiling and turns his head in a parody of "The Exorcist." He then lets go and lands on the bed. The only problem is that his body landing doesn't match the position it would from what we see on the ceiling. If he dropped down his face should be face down, body facing up and his head would be closer to the end of the bed. When he lands, his head is near the pillows, his body facing down and his head facing up.