Continuity mistake: During the fight inside the spider, West wraps one of Loveless' men in a chain and kicks him out the door. You clearly see that the chain comes completely off its roll and falls to the ground, presumably with the body. Yet later on in a wide shot of the spider you can see the body and chain still suspended from the spider. Then when it crashes, West uses the hanging body to save himself.
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.