Other mistake: When Homer drives through the barrier the second time (leaving the lake after dumping the silo) pay very close attention, his car smashes one portion of the barrier, but his car passes through a second portion of the barrier without breaking it. (00:23:50)
Other mistake: In the motel room, the poster of Alaska is not reflected in the mirror behind Marge. You can only see the little lamps next to the bed. (00:40:15)
Other mistake: On the close-up shot of the "Doomsday Clock" with "Sponsored by TIMEX" underneath, the clock is counting up from 1:33 to 1:34, rather than down. (01:08:05)
Other mistake: When Homer thinks he's out of the dome, he has a reflection, but Marge doesn't. (00:30:20)
Other mistake: For the car to be carried by the angry Springfieldians, there would need to be a big jump between the ground and the car, but from the car view there is no sign of that. (00:34:00)
Other mistake: Homer puts superglue on his hands and gets his hand stuck to his groin. He then uses his second hand with superglue on to get his hand off but that hand doesn't get stuck. (01:04:10)
Other mistake: Near the end of the movie Bart and Homer are on the roof. Homer hammers the nail into the roof then stands and the shingles are nailed to his leg, however, you can see that he did not nail it to his leg. (01:14:00)
Other mistake: When Homer is collecting firewood his footsteps start randomly in the midde of nowhere, with no tracks to the trees he came from. (00:45:55)
Other mistake: At the end of Marge's video message to Homer, Marge explains she taped the message over their wedding video. The video then shows the remainder of Homer and Marge's wedding. This is inconsistent with The Simpsons' Season 3 episode "I Married Marge" and Season 8's "A Milhouse Divided," which show Homer and Marge marrying at a chapel on the state line and later Homer and Marge alone eating cake together in a parking lot.
Other mistake: When Mr. Burns is talking to Apu, Doctor Hibbert and Chief Wiggum about supplying Springfield with power, he is writing with his right hand despite being left handed. (00:45:00)
Other mistake: When Homer falls through the roof into the house we see Grandpa sitting somewhere other than the ground floor or the second floor. The problem is the Simpsons' house has an attic on top of the second floor and below the roof. The length of the attic's floor and the house around it are totally the same, so really what we should have seen was the attic, not Grandpa sitting somewhere. (00:08:25)
Other mistake: When Marge is watching the recording of Grandpa on the cell phone, the camera changes positions suddenly after he says "Trapped forever." How could an old-fashioned flip phone pause like that? Also, in the 2nd view, it shows a floor-to-subject camera angle - the only way that could be possible is if there is a hole in the floor and someone's recording through it. (00:10:46)
Other mistake: When Homer kicks over the bomb, the time on the bomb decreases by half. Because of this, Krusty yells "Get outta here!" to Homer. However, Homer was standing in front of the bomb and Krusty was standing behind Homer, which means Krusty's view of the bomb was completely blocked, so he couldn't possibly have seen the bomb lose half of its time. He was definitely reacting to bomb losing half of its time, as he is shown looking straight at it just before he starts yelling at Homer.
Other mistake: When Homer is sliding down the rope, he knocks off several people climbing up. These people are never shown landing on the ground.
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)
Answer: I believe the joke is supposed to be that the way Texans speak is a language all its own.
Damian Torres