Character mistake: Towards the end of the film the Jackal, in disguise as the fictional one-legged, grey haired Frenchman Andre Martin, finishes setting up his sniper's nest and removes his beret, revealing that he has only dyed his hair grey where it protruded. He has a circular mop of his normal chestnut brown hair under his hat! This is an incredibly stupid thing to do - it is a perfectly normal thing for a policeman (or any other security operative) to ask that someone showing identity papers remove his hat if he is wearing one. The Jackal is a professional assassin who meticulously prepares for all contingencies - he isn't going to throw away his whole plan for the sake of a bit of extra hair dye. (02:10:05)
Plot hole: There is a barely credible explanation for the fact that a guest cannot be injured or killed by being shot in Westworld, but what about the vicious fistfight we see in the bar? People are injured or killed in bar brawls all the time, and this one was incredibly violent. How do they prevent guests from being injured or killed by the cutting and stabbing weapons we see in Medieval and Roman World? Guests are supposed to fight each other, not just robots - they cannot be 'programmed' to lose! Delos is going be sued into bankruptcy within a week of the first guest arriving. Quite apart from the legal position, think about the bad publicity! Who is going to pay the huge fees demanded by the parks owners when the media is constantly reporting on the guests who wound up dead or with life changing injuries?
Other mistake: During his conversation with the landlord of the pub he ends up staying in, Sergeant Howie makes it clear that he did not intend to stay on Summerisle overnight, that he had been delayed and so needed accommodation. Makes you wonder why he packed his pyjamas. He's wearing them when Britt Ecklund does her famous naked song and dance routine, and they are not new so we know he didn't buy them that day. When he arrived he didn't even think he'd be on Summerisle for more than a few hours - we don't see him with so much as an overnight bag.
Visible crew/equipment: Near the beginning of the movie, the old priest is in Northern Iraq and you can see the shadow of a microphone on his hat.
Visible crew/equipment: After Callahan removes the bomb from his mailbox, he looks up at a man on the nearby stairs. As a car drives by on the street, the lights from it cast the shadow of the boom operator onto the wall.
Plot hole: Swapping his dental X-ray records with his deceased partner won't convince anyone that Varrick is dead - then (as now) the patient's name appears on the X-ray.
Other mistake: In the intense outdoor battle scene at the end, when Bruce kicks a guy in the face three times in a row, one of the extras in the background cracks up laughing.
Factual error: On the night of 19 October 1933 the railroad workers begin betting whether A-One will make it to Portland on the 19. A quick closeup of the money changing hands reveals the $1's to have the Great Seal reverse (introduced in 1935) plus the motto IN GOD WE TRUST (introduced in 1957). Also, the green-seal Federal Reserve Notes and the red-seal United States $2 notes are of the types first introduced in 1934.
Factual error: When Clint Eastwood first goes to the barber shop, the barber very deliberately sharpens his razor the wrong way, flipping the blade with its sharp edge against the strop - this would instantly dull the blade. No real barber would make this mistake, but it's a common movie error.
Factual error: The kid is wearing a Texas Rangers baseball cap. The Rangers didn't come to Texas until 1972.
Continuity mistake: Shortly before Sol's death, Thorn rushes into the suicide center and talks to him from the control room above. When Sol pleads Thorn to listen, there's interference on the intercom. Now watch the control panel: The earphone cable on the left side dangles back and forth each time the "speaking permitted" sign flashes on and off, blatantly revealing the cheap trick they used to make the display flashing - they simply toggled the "on" and "off" frames. (01:17:30)
Revealing mistake: Right at the end when John is dying look at the texture of his blood. It is way too thin, almost like coloured water.
Continuity mistake: In the scene where Ka and Bee jump over the "wall" towards the end after attaching the bomb to the boat, they have nothing on their backs; but when they jump into the water, the 'holder' of the bomb is seen on their backs again and the woman takes it off then.