A close up as Miller lights his pipe in the first saloon scene shows that Nicholas Cage has used 3 matches at once, likely for a bigger flame on-camera.
Upon seeing a rash on Will's leg, Fred tells him "You better let it have some air. That'll creep up to your balls, make 'em swell like grapefruits." Yet the film is set in the early 1870s, nearly twenty years before grapefruit would be cultivated in the United States, and nearly forty years before they would become popular. Even if Fred had seen a grapefruit, he couldn't have expected Will to know what they were, let alone to use it as a frame of reference.
At minute 58:30 Charlie uses his left arm which was disabled before and his right arm, initially in good condition, is in a scarf.