Factual error: The sheriff and his posse raise huge dust clouds as they gallop down the road. But the stagecoach they're chasing, with four horses and four wheels, is on the same road and isn't raising any dust at all.
Continuity mistake: Curry takes his boots off and runs across a patch of very dusty, dirty desert. When he returns to put his boots back on, the white socks are perfectly clean with no dirt on them.
Continuity mistake: In the opening scenes of the chase, Heyes is wearing a vest, then not wearing a vest, then wearing a vest.
Continuity mistake: When they meet Carlotta, Heyes steps forward to greet her wearing his hat. The shot cuts to a different camera angle, and his hat is instantly off and in his hand, without time for him to remove it. (00:03:45)
The Clementine Ingredient - S3-E4
Factual error: Clem puts the paper photo into an envelope and licks the flap to seal it. Pre-cut, pre-gummed envelopes, though they'd been invented, were big-city luxuries rare-to-non-existent in the "wild" west - they were too expensive for most people (like Clem) to afford, especially in the economically depressed decades following the Civil War. You generally cut and folded your own envelopes and glued or sealing-waxed them shut. (00:33:40)
The Clementine Ingredient - S3-E4
Continuity mistake: Due to the insertion of stock footage, Heyes and Curry ride the short distance to Clem's house on three different sets of horses.
The Strange Fate of Conrad Meyer Zulick - S3-E9
Other mistake: When Doc Donovan reads the wanted posters, the physical description of Heyes mentions dark brown hair and brown eyes, which fits Pete Duel. However, by this episode, Roger Davis had taken over the role. He has light brown hair and blue eyes.
Continuity mistake: Heyes and Curry both lose their hats when they jump from the riverboat into the water and swim ashore. There's no time to go back and fish the hats out, even if they could find them, but by the next episode and for the rest of the season, they somehow have the same hats back again. (00:41:00)
Continuity mistake: Near the end, Heyes leaves the house with his gun strapped on, but when the camera angle reverses, he's not wearing it. It's back in the next shot, though.
