The movie, set in 1935, depicts executions in Louisiana being carried out by electrocution, but the Louisiana Legislature did not change the method of execution from hanging to electrocution until 1940.
Although Scotch tape was invented in the 1930s, it had a yellowish tint and would never have been used over a person's mouth. It did not have the adhesion of modern-day packing tape and would immediately come off from saliva. Rather, they would have used white cloth adhesive bandages that came on a metal spool that fit in a steel sleeve. Even early Johnson & Johnson Band-Aids were cloth with a sticky, white adhesive that would remain when removed. Clear packing tape was not widely introduced until the 1980s. Even the packing tape used in the 1970s, made of the same plastic, was brown.
The clock in the execution room is a quartz clock. The quartz clock was invented in 1927 by Warren Morrison and was not even used in laboratories until the 1940s. So it is implausible that a quartz clock was used in a prison in 1935.
Popular 40s/50s vocalist Eddy Howard is featured on three soundtrack songs, all recorded 4 October 1940 (five years after the movie's setting), with a small jazz band which featured pianist Teddy Wilson.
On the desk in "E-Block" at Cold Mountain, there is a small black clock. It is next to the telephone, and faces the wall behind the desk. When Wild Bill is brought into the cell block and the brawl ensues, the clock is knocked off of the desk. This action shows the clock clearly, and it is a Westclox Big Ben "Style 5". The Style 5 was designed by Henry Dreyfuss and introduced in 1939. Production continued until 1949. Since the movie takes place in 1935, that particular model of clock should not be there (especially given how worn it looks).
The guards are mixing a cup of RC Cola with some drug to knock Wild Bill out so they can take Coffey to the Warden's wife. Those bottles of Royal Crown Cola were not used in 1934 or 5, the time the movie takes place in, but were 1950s bottles. The earliest painted RC pop bottles has pyramids and a copyright date of 1936 on the label, and prior to that were likely plain, embossed glass bottles.
When Paul and Brutal place Percy in the straitjacket, they are using one with buckles. Straitjackets that use buckles were not introduced until the 1980's. Before then, they were the type that laced up through eyelets.
When Paul Edgecomb approaches John Coffey's cell after getting kicked in the groin, John Coffey asks him to come closer to the bars. When Eduard Delacroix warns Paul that he's not supposed to do that, Paul replies, "Mind your business, Del." But if you watch Tom Hanks' lips, he actually says "Mind your own business, Del."
In the scene where William Wharton is attacking the guards when first being brought into death row, we clearly hear the sound of Brutal whacking Wild Bill over the head just before he actually hits him.
Wild Bill shown laying on a mattress on the floor, after he tore up his cell, from which he gets up to request a drink of soda. After he is given the soda, he sits down on his bed which has a mattress. Shortly thereafter, he is again shown passing out on his bed.
During the entire execution of Eduard Delacroix, the generator light bulbs behind the partition are lit. This can particularly be seen in a cut with Brutal in the foreground. But when Percy gives the order "Roll on one" to Van Hay the lights are initially out when they cut to behind the partition.
When Brutal, Paul, and Henry lock Percy in the isolation room so that they can sneak John out of the prison to see the warden's wife, the position of the rag in Percy's mouth changes slightly underneath the packing tape in between shots.
In the scene when Percy is sitting at his desk reading a book on mental patients with the dirty magazine in it, Brutal and Paul come in and Percy jumps up closing the book and throwing it where it falls off the edge of the table. In the next shot when Paul picks up the book it is laying on the table opened to the page where the magazine is.
The sex of the mouse changes. When Mr. Jingles first appears, and then scuttles under the door way - the mouse is clearly male (distinguishing between the sexes of mice is easy because of the size of the genitals). However during the scene where John Coffey shares his cornbread Mr. Jingles is clearly a female mouse.
When Percy tells Del about Mouseville in Del's execution scene the hat has not been strapped on his head, yet when it shows a close up of Harry Terwilliger's face you can see the hat on his head and in the next scene the hat is no longer on.
The crumb from the cheese wafer that the guards feed to Mr. Jingles is lying on the floor after Percy throws his baton at it and is still on the floor when he starts chasing Mr. Jingles with a waste basket but is gone in the next shot when Percy throws the waste basket at the mouse.
Percy shoots WIld Bill firing all six cartridges of his revolver. When they subdue Percy after shooting Wild Bill, Stanton grabs his gun and ejects the spent cartridges on the floor. When the camera pans above Percy and the bad spirits leave his mouth, unfired cartridges are seen on the floor above his head.
After John Coffey finishes putting the tumor into Percy, Percy drops his baton onto the floor and no one picks it up. When he's walking toward Wild Bill's cell, the baton is hanging from a string wrapped around Percy's wrist.
In the execution scenes, the victims of Old Sparky convulse as if in a severe seizure as the electricity is rolled through them, however, in real life, this would not and does not happen. The constant flow of electricity causes all of the victim's muscles in his/her body to contract until the electricity is stopped. Additionally, the kind of screaming heard would be impossible because of this, as the screaming heard is the kind made with a fully opened mouth, not a neutrally positioned jaw that would come as a result of the contraction of both the jaw opening and closing muscles produced by the electricity.
During prison scenes the guards are wearing sidearms. Real prison guards would not wear sidearms in the prison population for fear that one of the inmates might grab it and hold the guard hostage or kill the guard.
When Eduard Delacroix is being executed, a lightbulb explodes on the mile (the one between the desk and William Wharton's cell). When Paul walks to John Coffey's cell afterwards, the bad bulb is hard to make out, but it is there.
You can see a smallpox vaccination scar on the upper arm of the murdered girls' father in the opening sequence of him running through the field. Vaccination was widespread in the USA by 1935, the time of the movie.
Wild Bill kidnaps the two little girls in the middle of the night. However in another flashback to the day the girls were taken, it is in the evening when the mother realizes they are gone, meaning almost a whole day would have passed by before they were noticed missing. This seems odd considering how young they were that no one would have checked on them earlier in the day or noticed the blood and cut screen on the porch door.
No live mice were used to portray Mr. Jingles. Rats were used to portray the mouse. Rats are more easily trained than mice. Props such as the spool used in Mr. Jingles trick were enlarged to make scaling look realistic.
After the botched execution, Brutus hands Percy an old Soda Acid fire extinguisher. The extinguisher is being held horizontally. The old style soda acid type extinguishers would automatically begin discharging the agent if the extinguisher was turned over onto its side, or turned upside down.