Dean Martin later said of John Wayne, "Someone else would have laid around, feeling sorry for himself, for a year. But Duke, he just doesn't know how to be sick. He's recuperating the hard way. He's two loud speaking guys in one. Me, when people see me, they sometimes say, 'Oh, there goes Perry Como.' But there's only one John Wayne, and nobody makes any mistakes about that".

This movie marked the return of John Wayne to work after having a cancerous lung and two ribs removed just four months earlier. He insisted on doing some of his own stunts to show the public that the illness hadn't slowed him down.

Filming was due to begin in October 1964, but had to be delayed until January 1965 after John Wayne was diagnosed with lung cancer.

George Kennedy recalled he was surprised to find that John Wayne still smoked cigars during filming despite having undergone major surgery, although he had stopped smoking cigarettes.

When John Wayne is dragged into the river, a child calls out, "Come on Dad!" This was his three-year-old son Ethan Wayne, who was watching off camera and knew how ill his father was. Wayne contracted a serious cold due to filming this scene, and narrowly avoided the cold worsening into full blown pneumonia.

Continuity

When the Elder boys are in town and decide to go to look at their old ranch, Tom has a scruffy beard. When they ride to the ranch and have a run in with the deputy, Tom is now clean shaven. They all ride back into town. When they reach town, Tom has his scruffy beard again.

When the Elders get on the bridge, the water has a strong current. Yet when Tom and Bud jump in to get more guns the water is like a mirror.

When John and Matt Elder are shackled together at the blacksmith's, the leg iron is bolted just below the top of John's boot. In the next scene after Matt's leg iron is fastened, John Elder's leg iron is wrapped around his pant leg instead of his boot.

When John Elder is watching his mother's funeral, he is shown from three different angles, standing in three different spots.

When he is seen watching the funeral, the position of John Elder's hands change between the long shot (hanging by his side) and the close shot (his left on his hip, his right on his gun). A rock visible behind him in the long shot disappears as well.



Factual errors

When the four brothers ride into town to settle Katie's affairs, the Texas flag is upside down.

When Bud says he is going with John and that they'll be famous like the Daltons, John replies that the Daltons were dead having been hung. Three of the Dalton brothers, Gratton "Grat" Dalton, Robert Rennick "Bob" Dalton, and Emmett "Em" Dalton all participated in a famous attempted two bank robbery in Coffeeville, KS on Oct. 5, 1892, along with two gang members, were gunned down and killed by town's people. No Daltons were hung.

The story takes place in Clearwater, Texas, and when John Elder asks the judge how long it would take to get to Pecos the judge says 8 or 9 hours. Pecos is more than 500 miles away from Clearwater and it would have taken more than a week to go that distance on horseback.

At the beginning and end, Katie's rocking chair is shown. The visual is accompanied by the creaking of the chair, as it rocks. But this chair is a simple two bar rocker. It is a solid one piece and has no mechanics in it to squeak. A glider rocking chair, which has suspension components, may squeak, but not Katie's type.



Incorrectly regarded as goofs

In what appears to be a previously used set - the four brothers are in jail, there is what has been referred to as a swastika drawn underneath the window next to John. The symbol seen here is a Native American design, called "Whirling Logs", and was used in Native American art long before the Nazis utilized it in the 1930s.



Revealing mistakes

John Elder fires 14 shots from a six-shooter without reloading.

When John Elder draws his pistol on the Sheriff in the graveyard, there are two guns. One is in his holster, and the other is in his hand. This was apparently done in an effort to make him look fast on the draw.

The man who John Wayne hits in the face with a stick is obviously not George Kennedy. It was in fact Wayne's own stunt double Chuck Roberson who doubled for Kennedy in that scene.

During the gunfight between John Elder and Morgan Hastings in the gun shop at the end, John looks up from behind the counter and Morgan fires a round at him. There's a glow on the counter where the bullet strikes the counter before the bullet gets there. This is where the small charge is that simulates the bullet strike.

When Morgan Hastings is conversing with his son at his ranch while test firing a rifle, he bends down to fire the rifle and places it on a pile of sand bags. The bolt of the rifle is in the open position throughout the shot and so can't be fired.



Anachronisms

When Tom is playing solitaire the cards he is using have the numbers in the corners. Cards at that time didn't have numbers in the corners, just the pips or face designs.

After finding out John Elder is in town, Morgan Hastings is target shooting with a shotgun, but the shells he loads appear to be modern types with red plastic casings.



Audio/visual unsynchronized

In the gun battle between the Elder Brothers and Hastings' henchman at the bridge, there aren't enough gunshot sounds to match the puffs of smoke from the guns.

When John brings in the rocking chair, bible, and basket to Mary, there is a group of people sitting around listening to a man playing a guitar. His hands do not match the music heard.



Crew or equipment visible

When Ben Latta leaps forward to catch the revolver thrown by John Elder, the cable that snatches him backwards (after being shot by Morgan Hastings), can just be seen trailing behind him.



Plot holes

It is unexplained why the four brothers did not meet up when the father was murdered a few months earlier.

Curley takes a very long time to walk across the street in order to interrogate Hyselman.



Character error

The sheriff is playing chess when his deputy comes in with Tom Elder's wanted poster. The sheriff's opponent, who is supposed to be the better player, moves one of his pawns backwards two spaces. Pawns can't move backwards.

John insults Bud for using the non-existent word "clumb" instead of the proper "climbed" in an effort to demonstrate why Bud needs to go back to school. But later, John himself uses the word "hung" in reference to a hanging when he should have said "hanged."

When Tom is taking Dave Hastings to the blacksmith shop, Tom and Morgan Hastings exchange about ten shots, including seven or eight beyond Hastings's gun shop. Yet nobody comes to see what's happening, even though the town is quiet and the townspeople are on edge.

None of the Elder brothers has a Texan accent.