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.
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.
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.
During the opening credits, the weather shows nearly gone snow in town, then followed by roads covered in snow and snow on the sidewalks. Also, during the credits, it shows it actively snowing and then not snowing and back again.
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 collected 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.