Continuity mistake: When Green Day finishes, in one shot the dice on the drums are gone, but the next shot, they are back on the drums. (00:02:50)
Continuity mistake: When Grandpa is freaking out in the church, at the point where he says "Trapped forever", Kirk (Milhouse's dad) is sitting normally. In the next shot, his arm is now holding onto the top of the seat. (00:05:40)
Continuity mistake: When Homer slides down the rope hitting people off it, Barney gets hit and falls to the side. A few seconds later the bomb falls down and Barney is standing up ready to catch it.
Continuity mistake: When the mob approaches Homer's house, it is undamaged. However, a few seconds later when everyone is out of the house, it is suddenly ablaze, and it is clear that it's falling apart. But when the sink hole sucks the house in a few minutes later it is undamaged, and no evidence of a fire is visible. (00:32:50)
Plot hole: There are two cars driving behind the EPA truck containing Marge, Bart, Lisa and Maggie. When Homer uses the bulldozer to try and break the family out of the truck, the two cars behind the truck don't notice the bulldozer trying to destroy the truck. There's no way they couldn't have not seen the bulldozer since they were just behind it. (01:00:05 - 01:00:40)
Other mistake: As Green Day's barge is sinking, the barge is showing turning sideways, but the monitor speakers on the barge don't seem to be affected by the barge turning. (00:03:50)
Other mistake: When Springfield loses all the power, Mr. Burns' manor (with the Happy Holidays from Mr. Burns sign on it) seems to have appeared out of nowhere. (00:44:00)
Continuity mistake: When the dome is being placed over the town, the church and Moe's Bar are shown right next to each other, but later on in the film, when Barney runs out of the Alcoholics Anonymous meeting at the church, Moe's Bar is nowhere to be seen. (00:26:30 - 00:48:30)
Answer: The family doesn't treat him very well, particularly Homer. He may have wanted some revenge on them. Grampa is also a little senile.
Phaneron ★