John reaches into the back seat of his car to retrieve a tax folder. Jacob approaches and greets John. When John turns around to return the greeting his hands are empty. In the next shot he once again has the folder.
When John watched the lottery results the announcer says it's for a $3.4 million prize. The screen shows the prize as being $6.4 million.
Ariel tells John to move King's Rook to Queen's Bishop three in his chess game. The piece he subsequently moves is, in fact, a bishop.
When John is handing his Dad a beer at the shanty we see his hand reach into the bag and pull out a beer. In the next shot we see his hand back inside the bag and hear it dislodge the beer from its holder.
When John puts the fish in the back seat of Max's vehicle, it is a largemouth bass. When Max finds the fish it is now a yellow perch.
The IRS at the time of the movie didn't audit a year if it was over ten years old. In the movie they said he collected for 20 years and eleven of those 20 were not claimed properly. That is past the ten-year mark. He had not been collecting for probably a number of years, so those years would not have been audited and they wouldn't be entitled to anything.
After John throws a fish in Max's truck, Max smells that "rotting fish" smell after a few days. Minnesota during ice fishing season (November, according to the story) would've been too cold for the fish to not only thaw out but to begin to stink. There were several inches of snow on the ground during this time of the film.
The time line for the mayoral election is inaccurate. Election Day is the first Tuesday of November. The movie begins just days before Thanksgiving and Jake is still campaigning for mayor. On Christmas they talk about him winning the election and within a few days he is already acting as mayor.
At one point you can see John Gustafson in his shanty listening to a record player, and Max Goldman in his shanty watching a small Black & White TV, yet neither shanty has electricity, as they are designed to be portable and quickly movable on sleds. This is obvious when Max pushes John's shanty across the ice and into the water with his car, as there are no electrical lines attached or being dragged along with the shanty.
John states that he was a teacher at Wabasha High for 39 years. Though Wabasha does have a high school, it combines with the town of Kellogg to create Wabasha-Kellogg High School.
John sprays Max' roof with water despite freezing conditions. This is not an error as John obviously removed the cover from the faucet and reconnected his hose. This is an old and very familiar practical joke in the north.
When Ariel first comes to John's house she suggest a chess move, but no one has told her who's move it is. If it is the other side's move her suggestion not only may not be a good move it may even be illegal.
At 51:45, when Gustafson slams his front door, the wall shakes, revealing it to be a thin setpiece.
When Max is pushing John's shanty into the thin ice zone you can hear Max also honking the horn. When the camera is on Max, however, his hands are gripping the steering wheel, the horn honking on its own.
Though the movie is set win Minnesota with presumably lifelong Minnesotans, nobody speaks with an Upper Midwest accent.
When Chuck, Max, and John are talking about Ariel at the bait shop, John says that Ariel came to see him last night at 1:30 am. Ariel came to see him two nights ago, not last night.
When John comes back from his visit with the IRS, he returns in a cab but doesn't pay the cab driver.