Big Jake is bucked off his horse and falls in a mud puddle. Later in the same scene, his suit is clean but his jacket arm is soiled.
Nine gang members ride to the ranch. One is killed. Seven ride away with "Little Jake".
The guy that helps Hank bring in the trunk at the train station is later seen dancing in the saloon at Escondero, wearing the same clothes.
After the shootout in the hotel room, the strongbox supposedly has its lock blown open by a shotgun blast, revealing its fake contents. However, only two shotgun blasts were fired in the hotel room and both of them were aimed out of the room: one killed the guy coming in the window, and the other one killed the guy coming in the door. No shots were fired into the room.
Throughout the movie, Jake's dog's coat changes color many times between black and brown.
Michael describes the automatic pistol as a Bergman 1911 with a magazine that fits into the "handle." Bergman made a model 1910 but not a 1911 and all of their automatic models positioned the magazine wells forward of the trigger, not in the grips.
About 40:44, the car explodes in midair as it goes off the cliff before it hits anything.
About 40:54, a second car is shot in the radiator, with a burst of flames and cloud of smoke. If a bullet had actually hit the radiator, there would have been no flames but a continuous cloud of steam from the water boiling in the radiator. As the car rolls to a stop and the people disembark, no steam at all if visible although an obvious large hole is seen in the grill where the squib blew up earlier.
After 36 minutes, just before Sam comes to visit Jake in his camp, all the horses' shadows are towards the camera, as they have the sun behind them, but Jake's shadow is towards a big rock, besides the horses. The sun can't be at two places at the same time in the sky. The shadow is created by a spotlight behind the camera.
When John Wayne stops the lynching of the sheepherder one of the men reaches to draw his pistol. John then calls his dog to attack and the dog grabs the man's wrist. With the time it took for John to sic his dog the gun would have been drawn by even the slowest draw and John would have been shot.
In the shootout near the end, O'Brien tells James McCandles, "I hear you killed two good men in a fair fight tonight. Is that true?" James replies, "No. Three, counting you." But a few minutes before, James killed Pop Dawson. Both were armed, both facing each other, which is the definition of a "fair fight." That makes the count four, counting O'Brien.
O'Brien was referencing the earlier bar fight with the two assailants. He might not have witnessed the shooting of Pop Dawson. The discussion was leading up to him putting his gun down and staging a draw off with James to see who was faster.
When Big Jake shoots the wounded bandit from the shower cabin, the guy growls in pain, drops his pistol and falls backwards, but there is not one visible wound or even a drop of blood on his body, likely because the squib or squibs did not blow on cue.
When Jake is seen riding his horse down the steep hill after Michael, dark gloves can be seen on his hands as he controls the horse. These gloves were not on his hands before he started down the hill, and this may be Wayne's double attempting this stunt.
Around 39:00, you see the dust from the camera vehicle kicking up over the lead car and the motorcycle. No glass is visible in any car. As they are in the lead, there would have been no one in front to kick up dust.
After Jake throws his son James into the mud, James pulls his revolver. It can be clearly seen that the chambers are empty.
Impossibly fast deer! When Big Jake challenges Michael to shoot a mountain buck, he says it is a quarter mile away. But then Jake says it's too late, because the buck starts running. Michael raises his rifle and takes aim at the running buck through his rifle scope at an approximate 60 degree angle to the viewer. In less than two seconds, Michael swings his rifle following the running buck to a nearly 110 degree angle and then shoots. A buck at 440 yards away and moving 50 degrees from the shooter in less than 2 seconds would be running at an astonishing 379 miles per hour! In reality, mule deer (which this deer clearly was) have a top running speed of 45 miles per hour.
None of the motorized vehicles are carrying extra fuel.
In the opening sequences, one of the hands tells Martha "I'm 42 years old and I fought in the Lincoln County War". Since the movie is set in 1909, he would have been born in 1867. The Lincoln County War occurred in 1878, so he would have been 10 or 11 years old.
John Wayne knocks out Patrick Wayne and Christopher Mitchum in the hotel room. Then he throws water on them to wake them up. A few moments later, their hair is dry as are their shirts.
After the shootout in the hotel room. The three dead cowboys bodies suddenly disappear. And no one in the hotel or from the town is seen during or after the shootout.
The amount demanded by the kidnappers is beyond absurd. While in 1971, $1,000,000 1909 dollars might have been close to $6 million (still an absurd sum for then), in 2020 dollars it comes to approximately $26 million. Not only is that an unrealistic sum, but Martha tells Jake that she has "many times more".
Not only is this a ridiculous amount, but there is also no way that any intelligent, responsible ranch owner would have this amount of cash in a strongbox in the attic. The cost of a house fire would have been devastating. It, quite naturally, would have been in a bank.
Not only is this a ridiculous amount, but there is also no way that any intelligent, responsible ranch owner would have this amount of cash in a strongbox in the attic. The cost of a house fire would have been devastating. It, quite naturally, would have been in a bank.
The motorcycle that is supposed to be an Indian Scout is a mid to late 1960s Montesa, possibly an Impala 175 Cross or a Cappra 250 that is modified with bicycle style handlebars and a box tank to look similar. The 1909 Indian Scout had a bicycle style frame with no suspension and narrow bicycle style tires, unlike the motorcycle in the film with telescopic forks hidden behind the rifle scabbards. The Indian Scout would have had either a single cylinder leaning to the rear or a V-twin arrangement, unlike the inline two cylinder leaning toward the front on the movie motorcycle. A kick starter is visible, which was not available, as it started by using the bicycle pedals on the Indian which are not present on the movie Montesa. Due to no suspension, jumps as were made would have resulted in crashes with a 1909 Indian.
When Michael is riding his motorcycle next to the Rangers' cars, there are wide modern-day tire tracks in the dirt.
The observation about Michael's blonde streaked hair briefly turning brown is a misinterpretation. Very light blonde hair looks much darker when it is WET. Michael's hair looks brown after the family fight in the hotel room because his head is soaking wet.
Michael is the only man in 1909 to have a streaked blond, mod hairdo, which also occasionally turns to brown, and then back to streaked blond.
After Sam Sharpnose comes back from checking if they are being followed, we hear Jake say, "We'll take a break here", but his mouth is saying something else.
When the rangers are ambushed, they shoot the driver of the car but when it goes off the cliff there are two bodies in the car. There is the driver in the front seat and someone in the back seat only though there was only one shot fired that hit the driver.
Towards the beginning of the movie when they're about to hang the sheepherder and Dog takes the man off his horse, the man is obviously wearing a pad on his arm so he doesn't get injured by Dog.
When crossing the river into Mexico, the camera is on the Mexico side looking toward Texas. The river is shown flowing right to left, but should be flowing left to right or west to east.
Before the Rangers set out after the kidnappers, Michael tells them that they are five hours away. He does not refuel his motorcycle before they leave. Presumably, there are no gasoline stations along the way, and no extra fuel is seen being carried. They should have run out of gas a long time before reaching the bad guys.
Jake's asks his ex-wife for 3 pack horses which are all loaded and then the sends for his tracker and says he doesn't need to bring a horse. Then the tracker uses one if the pack horses to ride. The remaining two pack horses would presumably be carrying all the gear but don't seem to have any more load. If Jake planned to provide the tracker with a horse he should have brought a spare riding horse.
When Wayne provides his knife to the thug to cut down shepherd Bernard Fox, he rides away without retrieving it.