Mostly because I’m not seeing anyone talking about it.
In one of the final scenes of the episode, Arya, posing as a serving girl, serves Walder Frey a meat pie made from his own sons.
She could have killed him and his sons numerous ways, but she chose this way for a specific reason.
Think back to a couple seasons ago. Bran, Osha, Hodor, and Rickon were fleeing Winterfell after Theon had sacked the castle. They stopped in an abandoned watchtower and started telling ghost stories, specifically the story of the Rat Cook.
For those who do not know the story of the Rat Cook, according legend, a King once paid a visit to the Nightfort, one of the main forts along The Wall. Due to some offense by the king, the cook killed the king’s son and cooked him into a pie which he later served to the unknowing king. The king enjoyed the pie so much he asked for a second helping.
The gods, angry with the cook, cursed him by turning him into a fat, white rat which could only survive by feasting on its own young. He was condemned to roam the halls of the Nightfort, surviving only on the flesh of his own offspring.
The gods were not offended by the murder, nor even that the cook had served the king a pie made from the flesh of his own son, for a man has a right to vengeance. What the gods could not forgive was that the cook broke the laws of hospitality, which are held to be sacred above all others, by murdering a guest beneath his roof.
This is apparently a common story told to the Stark family and would be well-known to Arya.
Walder Frey murdered guests beneath his own roof during the Red Wedding. He broke the laws of hospitality and was paid the Gods’ punishment.
