Valar Morghulis!! All Men Must Die!! But you need not die by reading SPOILERS. That'd be a horrible way to leave this world. So please don't scroll down if you haven't seen Season 6 yet.
All the fans started partying after seeing Arya cross another name off her list. Or I can say the most important one in her list as he killed more people dearest to her. Hostler Tully called him "The Late Walder Frey" and that's how we'll be recalling or mentioning him from now on. When we saw a good-looking girl pouring wine for Jaime and Bronn, most of us knew right at the moment that it was our Arya. I did expect that she will kill Walder and his sons but what I didn't expect was her serving Black Walder and Lothar to Walder in a pie. The moment I saw that, something ringed my memory bells and I had this moment of epiphany. It was the story Bran told Meera and Jojen in the last episode titled "Mhysa" from Season 3. It's the story of a Rat Cook who got that name for serving a pie to the king that was cooked using his son's parts. Let's take a look at that conversation again.
Bran : You ever heard about the Rat Cook?
Meera : No. Who's he?
Bran : Just a cook in the Night's Watch. He was angry at the king for something, I don't remember. When the king was visiting the Nightfort, the cook killed the king's son, cooked him into a big pie with onions, carrots, mushrooms and bacon. That night he served the pie to the king. He liked the taste of his son so much, he asked for a second slice. The gods turned the cook into a giant white rat who could only eat his own young. He's been roaming the Nightfort ever since, devouring his own babies. But no matter what he does, he's always hungry.
Meera( chuckles ) : If the gods turned every killer into a giant white rat..(Bran interrupts)
Bran : It wasn't for murder the gods cursed the Rat Cook or for serving the king's son in a pie. He killed a guest beneath his roof. That's something the gods can't forgive.
It wasn't for murder the gods cursed the Rat Cook or for serving the king's son in a pie. He killed a guest beneath his roof. That's something the gods can't forgive. - Bran
That's exactly what Walder did under his roof. The only difference is that it isn't just "a guest" but thousands of them. Robb, Catelyn and Talisa were the most important ones though.
And guess what? The gods didn't forgive that old moron and gave him the death he deserved. The most interesting part here was not slitting his throat but making him eat his sons that brings us to another part of the story.
The gods turned the cook into a giant white rat who could only eat his own young. He's been roaming the Nightfort ever since, devouring his own babies. - Bran
Majority of the stories and prophecies that are said on Game Of Thrones are metaphorical. This means that the story need not be exact so we don't have to worry about the reason behind Walder not turning into a giant white rat. But a part of it did happen. The part "eat his own young" turned out to be true. He did eat his sons. At least a part of them that was cooked into pie.
..the cook killed the king's son, cooked him into a big pie with onions, carrots, mushrooms and bacon. That night he served the pie to the king. - Bran
Now some of you might be wondering about the rat cook and Arya's role as they were similar. But like I said, these stories are just metaphorical.
Maybe, we can coin a new name for this story. Something that Bran's grandchildren will be telling to their grandchildren. Got a cool name for this story? Comment below.