The Citadel: Prophecies

III: 117 - Fool’s Blood, King’s Blood

"Fool's blood, king's blood, blood on the maiden's thigh, but chains for the guests and chains for the bridegroom, aye aye aye."

This mumbling from Patchface seems to match the aftermath for the Red Wedding quite well. The slaughter did not begin until the Frey bride of Edmure Tully was deflowered, thereby sealing the marriage beyond the possibility of easy annulment and Edmure and the surviving guests were chained.