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.
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.
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.
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.
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).
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.
While racism is shown and implied and even though the guards were not likely college-educated men, there is virtually no racist speech used in the film. Considering that this was 1930s Louisian, this does not seem to be possible.
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.
In order to protect Dean's family, the three guards specifically excluded him from the actual execution of sneaking John Coffey out so Percy could not implicate him. But when they throw Percy into the restraint room, Dean can be seen standing behind the others in clear view of Percy.
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.
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.
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.
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.
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.
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.
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 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 the warden's wife wore the necklace, I believe there were times it was not visible on her. When she gave it to Coffey, he is so much bigger than she, I was surprised it sat down so low on his chest. I would have thought that the necklace would have sat higher closer to his neck. In addition, she had to unclasp it to remove it from her neck but she was able to place it over Coffey's neck. Same necklace?
As Percy leads John Coffey into E Block, he continues to announce, "Dead man walking!" The phrase "Dead man walking" is usually announced to other nearby inmates and staff that a condemned inmate is being lead to their execution.
The homes shown in the film are fairly large for men working a state government job in the 1930s. While the warden's home would likely be a benefit from working at the prison, the rest of the homes were much larger than homes that would be owned today by people earning far larger amounts of money working for the prison system.
Although the voltage used for electric chair executions (2450 volts) would not be high enough to cause a current flow through an unsoaked sponge properly, it will just act as a resistor and limit the amount of current passing through at a time. That is why the electrocution took way longer than the required 15 - 30 seconds. The primary cause of death for Del was not via electrocution (brain death or organ failure) but through severe burns when the resistors overheat and caught fire.
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.
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.
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.