We can see that the cash register at the local store reads $2.22 before Ed Gein's purchase is rung up. When we hear the distinct sound of the cash reel mechanisms, the clerk tells Ed "that'll be $2.22" even though nothing moved. A few days later, Ed steals the cash register and puts it in the back of a delivery truck, and the readout still shows $2.22. Clearly, a non-working cash register that the producers tried to get too much mileage out of.
Although Ed Gein has often been referred to as having been a cannibal, he never confessed to such nor was any evidence of actual cannibalism ever found.
The text at the film's ending says that Ed Gein died at the age of 78. He was actually 77 years old when he died, one month before his 78th birthday.
Both Ed's mother and, later, Ed himself read passages from the Book of Revelation in the Bible (primarily focused on the 'whore of Babylon')... but they are reading from about the first 10% of the book, while Revelation is the very last part of the book. However, Augusta and Ed often read the story of Noah, found in Genesis.
Ed Gein, and most of the other characters in the film, speak with southern accents, but Ed Gein was from Wisconsin, and the film takes place there.
When the bartender is discovered missing, a trail of bloody one dollar bills is shown using Federal Reserve Notes, which were not created until 1963. In 1954, they would have been Silver Certificates.
After Ed Gein kidnaps the bartender, he takes her home in his truck. On the way to the house, they pass a vehicle traveling in the opposite direction. The vehicle has rectangular headlights, a type of headlight which was not found on vehicles in the 1950s.
A gas pump says "5% sales tax added." The film takes place primarily in 1957; Wisconsin did not have a sales tax until 1962, when it was 3%. The sales tax did not reach 5% until 1982.
Actors in several scenes can be seen breathing while they are
lying prone, even though their characters are supposed to be dead.
A mountain range is seen looming over Plainfield, Wisconsin, which as its name suggests, is on a plain.
After Mary's death they are given to understand that Ed was a cannibal, but Ed was never a cannibal, that was a hoax.