Continuity mistake: After Gordon detaches West's boot off the magnetic collar, West raises, extends his right arm and hugs Gordon. A shot later his right arm is lowered.
Continuity mistake: When Gordon tries to detach West's boot from the magnetic collar, the position of his right hand on the boot changes positions depending on the shot.
Continuity mistake: When West's boot gets stuck to the magnetic collar, in the close-up shots it is firmly stuck, but in the wide angle of him falling backwards it is totally loose. This keeps swapping back and forth.
Continuity mistake: While trying to detach the magnetic collars, West's right hand is either holding Gordon's collar or not, depending on the angle.
Continuity mistake: After the mudpit scene, when the magnetic collars get attracted to each other, Gordon's jams on top of West's. When the shot changes it's the other way around.
Continuity mistake: When West and Gordon, with their metal collars on, fall on the huge puddle, the amount of mud on West's hat changes drastically between the first and second.
Other mistake: Obviously, the spider needed a crew inside to manage its operation (feeding the boiler pressure going to keep it moving), but after West dispatches them individually, the spider seems to be able to run on its own when West and Gordon head back to Washington at the end of the film.
Suggested correction: There are still crew operating the spider, you just can't see them. Also, it's possible the thing is mostly automated, might need only 2 or 3 people in total.
Continuity mistake: In the cornfield scene before the flying razor discs are launched, Gordon's fingers change positions on a note he is holding as the scene cuts to different angles of West and Gordon.
Continuity mistake: Gordon's train dodges Loveless' train-tank shot by going around a bend. In the shot right after the dodge, we should see the bend that they just passed, but all we get is more straight tracks.
Factual error: The 80 foot mechanical spider leaves Arches National Park and seems to get to Promontory Point in almost no time at all - that's 312 miles.
Continuity mistake: When Arliss Loveless makes his appearance at a gathering, a giant bust of Abraham Lincoln is wheeled out. The head on this bust explodes and we see Loveless's head pop out in place of where Lincoln's was. When we see a close up of it, we see what was left of the bust around Loveless's head, yet instantly afterward in a wider shot, the remains of the bust disappear.
Other mistake: After the water tank collapses, for several seconds there's an angle on West and he is still floating horizontally as if nothing had happened. A couple of seconds later he finally slides downwards.
Revealing mistake: When the saw blade thrower begins powering up after Jim West steps out of the magnetic boundary, the gears beneath the saw blade rise and begin to spin, which are meant to engage the saw blades' rotation, but in a single frame, these gears are shown instantaneously back in their resting places, as the saw spins on its own freely before being flung from the machine. (01:02:20)
Continuity mistake: After the cornfield scene and the heroes fall into the mud river, their clothes and metal collars are seen to be covered in mud. In the next scene featuring them, their clothes are muddy but their metal ring collars are totally unmarked.
Factual error: In one scene Jim West is walking up to the White House. There is a cast-iron gate surrounding the White House, as there is today, but he gate was not added until the 1930's.
Factual error: The nitroglycerine would have exploded when McGrath's men threw it roughly onto the cart, leaving no risk of it exploding later when West makes his comment that this is not the way you transport nitro.
