Other mistake: The credits for the Tarleton brothers in the opening credits have the twins switched with their actors. George Reeves doesn't play Brent, he plays Stuart. You know this because in the opening scene the two boys are talking about the party and asking Scarlett for dances, and George Reeves points at his brother and calls him "Brent."
Continuity mistake: In the scene showing guests arriving at the Wilkes' barbecue, you see buggies and carriages driving through the front gates and up the drive toward the Wilkes' home. The carriages clearly create shadows on the ground, but not on the stone pillars of the gates. This is because when the movie was filmed, there were no actual gates. The gates were later "painted" into the frame. Proving someone forgot to "paint" shadows onto the pillars. (00:17:15)
Continuity mistake: The shadow scene in which Scarlett and Melanie care for the wounded in the Atlanta hospital was filmed with two doubles. Since Leigh and de Havilland were standing at the wrong angle to cast the shadows, two stand-ins were positioned in front of the high-intensity light. The shadows of the doubles were reflected on the wall behind the stars, and the result was a stunning visual effect. Yet upon a closer look, the gestures of the stand-ins are not totally synchronised with the movements of the stars. (00:56:30)
Continuity mistake: When Scarlett is attacked in the woods on a bridge while on her way to the lumber mill the buggy very nearly goes off of the bridge backwards. Then Scarlett faints, but when the camera returns to the full shot of the buggy, suddenly it is squarely in the middle of the bridge and in no danger at all of falling over the edge.
Continuity mistake: While our protagonists flee from the burning Atlanta the carriage stops. A bearded soldier walks by carrying another man. A few moments later the camera focuses on a young man who collapses and is being picked up by exactly the same guy who was carrying him already. The mistake wouldn't be as pronounced if it weren't been one of the few instances where action by extras is highlighted. (01:23:25)NancyFelix
Continuity mistake: In the scene when Rhett is saying goodbye to Scarlett before he leaves her on the road to Tara alone, he throws his hat behind him onto the road and takes Scarlett into his arms. However, a few moments later, he picks the hat up from the fence at his side along with his coat. (01:26:55)
Continuity mistake: When Scarlett undresses for her nap after the 12 Oaks barbecue, she unties a small bustle from around her waist. She didn't have this bustle on when Mammy helped her dress for the barbecue earlier that morning.ANTLYN
Revealing mistake: After Frank Kennedy's death Scarlett is sitting in her room, "mourning" and drinking. When she hears Rhett's carriage she goes to the window. In this moment you see shadows, either from crew members or equipment, cast through the room, especially visible on the bottle on the table. There is also some funny shift of the backdrop outside the window. (00:55:35)NancyFelix