Some of the guests at the Red Wedding are shown being killed and being alive in different shots, inconsistently.
As Arya witnesses the slaughter of Stark soldiers, she is hiding behind some barrels. Arya then moves forward and hides behind an upturned table and witnesses the slaughter of Robb's dire wolf. In the very next shot, Arya is shown once again peering past the barrels, moving to hide from the approaching Frey soldiers. The following shot shows Arya back behind the table, when the Frey soldiers actually move past her.
When Catelyn is looking at Roose Bolton's arm resting on the table, an inner sleeve appears between shots, even though he has not moved his arm.
Robb says that Catelyn begged him not to send Theon to negotiate with his father. Actually, Catelyn never objected to send Theon as an envoy on behalf of Robb: she only disapproved of the idea of forming an alliance with Balon Greyjoy.