Other mistake: During the scene in the banquet hall, as Tormund says "most people get bloody murdered, they stay that way", look at Daenerys in the background - a disposable coffee cup is on the table in front of her. This brown cup with a white plastic lid is nothing remotely like the style of cups they're all drinking from in the scene. HBO acknowledged the slip up and digitally edited it out on streaming services, reruns and future DVD releases.
Visible crew/equipment: When the horse carriage is ambushed, just as Princess Abigail can be heard screaming "Please, help me", the camera pans downward and a horse wrangler wearing a blue baseball cap can be seen in the lower left hand corner, hiding behind one of the horses. (00:03:20)
Other mistake: After the turkeys start attacking in "The Running of the Turkeys", Mr. Fishoder and his brother start running. In that clip a Turkey pops out the side of a guy's head. Look in the mid lower right side. Looks like a design error. Pretty big error, no slow down needed to see it. (00:05:20)
Continuity mistake: When Jackie and Martin are saying hello to the boys in the garage, Jackie's hands are constantly changing from open to closed fists between instant cuts with no time to open/close them. (00:01:40)
Continuity mistake: When Dave enters the room with champagne glasses to celebrate his terrible idea, in a brief shot as he enters he's holding the glasses upside down. We cut to the other angle when he asks Alex to help him, and they're now held the right way up. As she takes them off him the angle switches again, and they're back to being upside down. (00:12:00)