When Daenerys' mare dies in the Red Waste, it falls on its left side; when Daenerys runs to it, it is now on its right.
During the duel between the Hound and his opponent, each of them has a mace in his right hand and a shield in his left, but after the camera cuts to show the scene from a higher elevation - they have switched hands, showing that one of the cuts has most likely been flipped.
Jaime tells Robb "three victories don't make you a conqueror". Actually, Rob won two battles: the Battle of the Whispering Wood and the Battle of the Camps.
Robb confronts Jaime about pushing Bran from the window, although he had no way to know that; the only ones who know are Jaime and Cersei, and later Catelyn and Brienne.
In fact, Jaime confessed to Catelyn in the previous episode to be the one who pushed Bran. As both Catelyn and Robb were present at the camp at that time, though not shown, she most likely will have told her son about this. However, Jaime didn't tell about the reasons for the deed, so this part is speculation or deduction raised by the letter about Jaime's incestuous relationship that had been sent by Stannis earlier.
During a scene with Cersei and Joffrey, Cersei's necklace changes direction with the lion emblem facing backwards in several shots.