On the movie marquee (which is very 50s for a 1940 S.C. neighborhood theater) announcing the picture Li'l Abner (1940) one of the stars is identified as Jeff York though he appeared in the film using his original stage name of Granville Owen. He wasn't credited as Jeff York until after WW2 in They Were Expendable (1945).
Vintage scene with modern wood: during the riverside rope swing scene (circa 1940) there is a momentary glimpse in the foreground of a "telephone pole" style dock piling. Such pilings existed then, but the wood's all-around light green coloration is distinctive of modern "treated" wood soaked in chromated copper arsenate (CCA). A 30's pole should have been brown or weathered-gray (or, if creosote-soaked, black). CCA-treated wood didn't become commercially available until at least 40 years after when the scene was meant to be. In the mid-late 2000's some municipalities began banning the green toxic wood preservative.
When the band is playing on Noah's front porch and his father is playing the spoons with the band, as his father gets up to dance with Allie, he lays them down, but the sound of the spoons playing can still be heard in the music.
When Noah and Allie in the Windsor Plantation, after Noah explains about the significance of the stairs, we can hear Allie say, "This place is gigantic," but her mouth doesn't move until a few seconds after it was said.
When Noah jumps into the Ferris wheel seat that Allie and a boy are sitting in, we hear Allie's voice yell, "Get off me!", but Allie's lips do not move to say the words. While the words are said, Allie's mouth is simply open, as she is gasping.
When Allie and Noah are in the boat (just before it starts to rain), Allie's fringe/bangs are curled up tightly. A few moments later (when it begins to rain), Allie's fringe/bangs are perfectly straight. This could not have happened so quickly.
When the older Allie and Duke are having the candlelit dinner for two, Allie is wearing a plaid shawl over her red jacket as she begins to sit down. In the next shot of her seated, the shawl is off, with no time for her to have removed it. In the next shot, it's back on again.
When Noah and Allie are sitting on his front porch talking, Noah stands up angrily and throws the chair he was sitting in down, with the flowers falling on the ground. In the next shot, the chair is back up and the flowers are on the arm of the chair.
When they are lying in the street, their position moves from dead center of the road (they are in line with the center line) to being over in the right-hand lane when the shot moves from tight to wide.
While Noah and Allie are out in the boat and it begins to storm, Allie's eye make-up is smudged and running down her cheeks. As they run into the house, and both during and after their love scene, her make-up is fine. Also, both Noah and Allie have soaking wet hair when they enter the house, but by the time they are undressed a minute or two later, their hair appears to be dry.
After Noah and Allie get in the fight by her car at the end, he has his hands on his heart then walks towards the back of the car turns around and puts his hands on his head. About two seconds later she pulls away and he is in front of her car with his hands on his head.
When Noah takes Allie to the plantation for the first time she is instructed to stay outside. When she looks at the river into the moonlight her silhouette reveals flowing curls, and when she turns around her hair is slightly curled at the ends, but not nearly as much as 2 seconds earlier.
When Lon proposes to Ali, we see that he has not slid the ring on her finger. It is just resting at the tip of her finger. But when he jumps up a second later to run up to the bandstand, the ring is completely on her finger with not enough time passing for Lon to do so.
When Allie and Noah were lying in the street, they were in the center. A moment later, without getting up, they were in the right- hand lane. Then, again without getting to their feet, in the next shot, they were back in the center of the street.
When Allie walks into Noah's barn and admires his carpentry, the right side of her blue scarf changes from behind her back to her front to her back again in continuous shots without the film ever showing her physically moving it herself.
When older Allie and Noah sit down to a candlelit dinner, Allie is wearing her shawl over her jacket when she starts to sit, the shawl gets in the way & the next angle, with no time to remove the shawl, it is gone.
The goof item below may give away important plot points.
Noah has brown eyes (contacts to match Ryan Gosling's eyes with James Garner's) but when Noah is trying to stop Allie from leaving by standing in front of her car his eyes are shining blue in the sunlight.