After Katherine is covered with molasses and feathers, including her hair, during the Indian "attack", McLintock goes to see her 5 minutes later and she greets him with clean dry hair and skin, wearing new corset, slip, etc. While she might have been able to change her garments in that time, there is no way she could have gotten molasses and feathers out of her hair or off of her hands.
During the fight between Dev and Ben, G.W. comes out carrying the whiskey and there is clearly a poorly repaired crack in the wall next to the door. Later, when Ben dives at Dev and misses he runs into the undamaged wall and creates the crack that was there when G.W. walked out of the door earlier.
In the long fight scene at the end, Katherine flies out of a window and lands in a trough of water. After that, trying to escape G.W., she falls into the dusty and muddy road. But still, in the next scene her underwear are clean white - and dry.
The first man into the mud pit during the fight scene, slides down the hill toward a brownish-reddish muddy water pit, then in closeup he slides into chalky gray water.
A tipsy McLintock is trying to walk Katherine upstairs while swigging from a full whiskey bottle. They fall to the bottom of the stairs and the bottle clearly spills. Katherine picks the bottle up and bops McLintock on the head with it, then it becomes a full bottle again just before she throws it against the wall and it shatters.
The greeting in Comanche is "maruawe". But the "Comanches" greet each other (and are greeted by McLintock) with "yatahe", which is a Navajo greeting.
G.W. suggests to Birnbaum that the solution to his chess problem is "queen's bishop to king 4". This is an impossible move, regardless of where the pieces are.
When GW and Drago are driving the barouche into town early in the film, there is a line of poles leading from the house, across the road, and through a pasture parallel to the road after it curves. These are either electric poles or telephone poles, yet the house has neither electricity nor a telephone.
When the band is playing upon Becky's arrival, the music and the drums play but the drummer's beats are nowhere near hitting the drum; he misses by several inches.
In the store where McLintock is chasing Katherine, the part where he crashes into the baskets is very clearly done by stuntman Chuck Roberson and not by John Wayne.
When Devlin is driving the buggy to take Matt home from the McLintock's with Becky the scenery is passing by much faster than a horse could possibly travel.
The band music being "played" for Becky's arrival has a clarinet in the score, but no woodwinds are shown in the group of musicians.
In the opening credits there is an artist's rendering of the town of McLintock, with signs for every building indicating that every business in town is owned by McLintock. The sign on one of the buildings misspells McLintock as "McClintock."
All the cans in the general store are clearly empty. The hollow sound of empty
cans bouncing off each other and the floor is easily heard as the shelves are tipped
during the brawl with Katherine.
McLintock and Katherine each have blue eyes, but their daughter Rebecca has brown eyes. Her eyes should be blue as well.
In the mud fight scene, a person is seen in the background wearing a modern business suit. In the same shot, there's also a person wearing sunglasses.
During the rodeo scene, a 48 star flag (6 rows x 8 columns) is shown. If this area is still a territory, it's not Alaska or Hawaii. Before Arizona and New Mexico became states, there were 46 stars.
During the rodeo, an evaporator cooler on the roof in the background is visible.
When G.W. is hunting, he reloads, but the shells he is using are plastic hulled, not the paper or the wax impregnated shells that would have been used during the time the movie is set. Plastic hulled shells were introduced by Remington in 1960. Remington used green plastic in their shells, so the movie was more than likely using modern Remington plastic hull shells.
During the rodeo scene you can clearly see a 48 star flag (6 rows x 8 columns). Before Arizona and New Mexico became states, there were 46 stars.
When Junior Douglas is singing with Becky at the McClintock house, he isn't really playing the instrument. His hand movements are completely out of rhythm with the music. Nevertheless, Jerry Van Dyke was an expert banjo player.
In the famous chase scene near the end of the movie, when Katherine tries to escape from G.W. into an alley behind the general store, the shadow of the camera as it zooms in for her closeup is clearly visible against the store wall on the left side of the shot.
During the fight at the mudslide, when Agard is in the mining cart headed for the slide, the cable pulling the mining cart is clearly visible.
The real-life "Mesa Verde" extends south into New Mexico (a territory at the time of the film), but scenes show saguaro cacti which grow only in the mid and southernmost part of Arizona and northwestern Mexico. Being a fictitious story, the "Mesa Verde" in the film may well be a fictitious place, as the precise location is never given. and allowable under artistic license. The term itself means "green table" and may have been used to describe any mesa with plant life on it. More likely, though, is that this story was filmed in Arizona because 1) there's a studio there (Old Tuscon Studios) and 2) to use the saguaro as a symbol of the old west, a common practice in Hollywood at the time.
Davey hangs the "Welcome Home" banner for Rebecca the wrong way. It can't be read from the approaching train or from the passenger platform, but only from the street looking back at the station. (In other words, only from the point of view of the camera, not the characters.)
The fight at the mud pit took place in the morning, yet when G.W., Drago, and Katherine come home, it's nighttime and they're still covered with mud. It's doubtful that they would go all day covered with mud, especially Katherine who is very persnickety about her appearance.