(at around 1h 2 mins) At the medical office, the physician introduces herself as Dr. Chu. In the credits, she is Dr. Chang.
When Walt drinks beer in Sue's kitchen, the level of the beer gets higher the longer he drinks it.
The cigarette burn on Thao's face changes several times.
Walt has Thao wait until 4PM to come to his house to plan their action against the gang that shot up Thao's house, beat and raped his sister, Sue. He mowed his lawn that day, so it must still be summer. He locks Thao in his basement while he goes to the gang house alone. The sun is shining brightly. He calls Sue later and has her release Thao. The sun is still shining when she runs to Walt's home
from next door but it could be near twilight. Thao rushes out to find Walt. Walt does not arrive at the gang's house until it is dark. Thao and Sue arrive in Walt's Gran Torino but only after Walt is dead. Too much time elapses for them to get there from Walt's house.
(at around 14 mins) When the Hmong gangbangers drive up to the Mexican gangbangers, Spider drives forward, then drives in reverse without changing gears. Then a break in the scene shows his car's backup lights.
(at around 1h 11 mins) Walt tells his neighbors that he installed the steering column in his Gran Torino in the factory at Ford. The Gran Torinos of that time were made in Lorain, Ohio. None of the Torino models were ever assembled in any Metro Detroit area Ford plant.
Walt's medical form lists date of birth as February 1930. When his family celebrates his birthday with him, the grass is green, and he joins his neighbors for a cookout. That isn't February in Detroit.
Walt's license plate has three letters, followed by three numbers followed by one letter. Michigan license plates have three letters followed by four numbers.
Throughout the film it's revealed that Walt served with 1st Cavalry Division in Korea. At about the six minute mark his grand kids are looking through pictures and see one that reads 3rd platoon E Company. The United States Cavalry uses Troop instead of Company and has done so since 1883.
(at around 40 mins) Kowalski's daughter-in-law gives him a Walker amplified phone, so the curly handset cord should be plugged into the side, not the back.
Walt says he used the M1 Garand rifle in Korea. U.S. Military personnel are usually not allowed to keep their service weapons. However, some rifles, identified by serial number, were available for purchase through the Civilian Marksmanship Program after they were deemed obsolete or unfit for service. Enlisted and commissioned personnel also frequently "liberated" their weapons.
(at around 1 min) In the church, Walt's grandchildren genuflect (kneel briefly and make sign of the cross while facing the altar). In the Catholic religion, the cross is made with the right hand. The granddaughter crosses herself with her left hand. However, the grandchildren were established as disrespectful, both in attire and behavior (one even parodies the spoken prayer), so they could very likely use the wrong hand.
(at around 1h 3 mins) The medical form shows Walt's marital status as "married." The film opens with his wife's funeral. It is Walt's first visit to the medical center since his wife died. Based on the conversation with Dr. Chu, it had been more than 3 years since his last visit (long enough that he wasn't aware that his former physician Dr. Feldman had retired, and been replaced by her). With all that was going on in his life at the time of that visit, he could have simply forgotten, or not cared, to update his marital status.
When Walt touches the little girl's head, the Hmong react very negatively, and Sue tells him that is wrong. Several scenes earlier, Kho Khue patted the baby's head, and no one reacted. Certain elders have the right to touch people on the head, including an elder shaman performing a soul-calling ceremony during a birth celebration. Also, when Sue musses Thao's hair in the back yard, she musses the side of his head, behind his ear, not the top.
(at around 1h 3 mins) While Walt is on the phone with his son, the medical forms show Detroit, and a Michigan ZIP code, but lists the state as California. If you look closely, the California address is Walt's brother, as next of kin.
(at around 5 mins) The sides of the folding chairs flip by the time Walt takes the 2 folding chairs from the basement to the upstairs; the curvatures of the chairs clearly show this.
(at around 1h 3 mins) When you see Walt's hospital admittance paper, it lists his birthday as 02-10-1930 and his age as 68 years old. This would have the film taking place in 1998, but many early to mid 2000s model cars appear in the film.
(at around 1h 35 mins) In the bathroom scene when he is bathing and smoking, the reflection of the camera man's legs are visible on the bathtub.
(at around 1h 3 mins) When Walt speaks with his son on the phone and the camera pans to his hospital admittance and patient information, the patient info shows his city and state as Detroit, MI but the admittance shows Detroit, CA.
(at around 1h 3 mins) The address 2264 Vine Street appears three times on Walt's hospital admittance form as Walt's employment address, Walt's son's employment address, and the insurance company's address.
(at around 35 mins) When Walt rescues Sue and Trey from the three thugs, he tells Trey that he should not have said "bro" to them. This would have been impossible for him to know; he pulled up to the stop sign after the incident.
During Walt's second phone conversation about his medical records, a boom mike appears in Walt's son's house, above the kitchen table.
When Walt and Sue start to sit to talk on Walt's back porch, the boom mic appears ever so slightly.
(at around 1h 35 mins) In the bathroom scene, Walt says to the dog to give him a break because it's the first time he's ever smoked in the house. Actually, he smoked the night before when Father Janovich was with him inside the house and they also drank beer.
(at around 1h 3 mins) The medical forms list Walt's address as 5962 Delco St. When Walt stands on his porch, his house number is 238.
(at around 49 mins) When the Hmong ladies feed Walt in Sue's kitchen, Sue's mother Vu puts a large spoon into a bowl of salad, then moves to transfer the contents to Walt's plate, even though most of the salad fell out of the spoon back into the bowl. Either the actress either didn't notice, or she decided to keep going with the scene.
(at around 1h 1 min) Walt visits his doctor's office in February. The calendar is open to June.
The front license plate on Walt's truck is missing. Michigan doesn't require a front plate, but it looks it was recently removed. That wouldn't make sense, since he likely bought the truck new.