Continuity mistake: When Jake rides back to the house where his wife was abducted, he pauses and looks at the ruins. The hole in the roof which was blasted by the aliens is wide open to the sky with no ridge beam. A few minutes later, during the flash back scene, he watches the aliens pull his wife through the wide open roof hole. He then steps below the opening to gaze up and there is now a large beam across the roof opening.
Other mistake: Just as the preacher finishes stitching up Jake's wound, a shot rings out from the street, and everyone goes outside to find Percy Dollarhyde drunk and shooting up the town. Percy is right-handed but holsters his 6-shooter revolver on the left, and this appears to be his only sidearm. Even if he did carry another 6-shooter, that wouldn't explain how he fires 13 shots in this scene without reloading.
Continuity mistake: In the scene where Daniel Craig and company are chasing after an alien and arrive at a canyon while being intercepted by some bandits, Olivia Wilde can be seen getting off her horse and in an instant, on the next shot, she's got her feet on the ground with her arms in the air. This is on the Extended Blu-Ray version of the film.
Continuity mistake: During the film, Daniel Craig's character rides out to the house where he last saw the woman he was in love with. During the wide shot showing him on his horse riding toward the camera, the device on his wrist is missing. It is obvious if you are paying attention, as he is using the arm which is supposed to have the device to hold the reins of the horse.
Continuity mistake: When Jake is being hit in the face, he has blood on the right half of his face by his mouth. Quite a lot running from his nose to his chin actually. The next scene he is on the ground and no blood is by his mouth.
Continuity mistake: There is a moment where the camera pans out from everyone on their horses, and the main characters are seen closer to the front. The hat of one of the main characters flies off, but in the next shot everyone has their hats.
Continuity mistake: When Jake and Woodrow escape from the cave, tons of dust from an explosion hit Jake's left side leaving him looking like he just came out of ground zero, next scene clean as a dirty cowboy can be.