Goofs

When the black shadow creature enters the room and stabs Renly in the chest, the camera is facing the mirror and shows the blade entering the right side of his chest (it is on the left side of the screen but the mirror image translates to his right side). When the camera changes to a front view, the blade is shown impaling his left side/heart.

Before Brienne swears her oath to Catelyn, she is seen leading a white horse. The horse initially has a muddy left-hindquarter, but the next time it is seen within the same scene, there is no mud.

Jaqen H'ghar tells Arya that the "Red God" is owed three deaths. Some believe this to be a goof, as Jaqen does not worship R'hllor but the Many-Faced God. However, George R.R. Martin has clarified that as Arya rescued Rorge, Biter and Jaqen from death by fire, it is the Red God (just one of the faces of the Many-Faced God) to whom three deaths are owed.

Xaro tells Daenerys "Daenerys Targaryen, first of your name," although according to the novels, there were two other Targaryens named Daenerys: a daughter of Jaehaerys I and a daughter of Aegon IV. It is not an error, though: the two aforementioned Daenerys never ruled as queens, so Daenerys Stormborn is "the First of Her Name," not the third.

Bronn tells Tyrion "Not after what he [Joffrey] did to your birthday present." The correct Westerosi term is "nameday," not "birthday."