Continuity mistake: At the beginning, Eastwood dismounts from his horse to rescue the calf lying in the river. His horse is left standing in the river with the water up to his knees. When Eastwood places the calf on dry land, his horse is standing nearby. The horse's legs are dry.
Continuity mistake: During the opening credits, when titles are appearing under Eastwood's swinging feet, you'll see the footage of the swinging feet reverse itself at least twice.
Continuity mistake: When the cowboy comes riding up to Cooper and Sheriff Calhoun yelling about a murder, the sheriff grabs the reins of the cowboy's horse. Subsequent shots show the the sheriff's left hand either resting on the butt of the cowboy's rifle, sometimes not.
Continuity mistake: In the bar, when Marshall Cooper tells Reno he is under arrest, Reno pours another shot of whiskey. The shot glass is only about a quarter full. Cooper then puts out his cigar in the shot glass, which is now half full from a different camera angle. The amount of liquor in the shot glass changes from half full to barely a quarter full from one shot to the next. (00:35:00 - 00:36:00)
Continuity mistake: The first hanging scene in town, after Clint is cleared; and the real bad guy is about to hang. The hangman walks down the steps, you can see a long stick through all the rings (multi-trap door release); but when the judge nods his head, the hangman is only grabbing one ring.
Continuity mistake: Just before the hanging of the six, the video shot of the 18-year-old rustler shows his hair is parted on the right side. The video shot as the hanging begins shows his hair parted on the left side.
Continuity mistake: When the blacksmith looks up and recognises Jed, he is standing in front of the fire ready to put the horseshoe in. After Jed dismounts and the camera cuts back, the blacksmith is standing a few feet to the right of the fire.