This article contains major spoilers for the Season 2 premiere of HBO’s “House of the Dragon.”

It may not be the Red Wedding. But “Blood and Cheese” — as fans of the George R.R. Martin books call the closing event in Sunday’s episode of “House of the Dragon” — is likely to be a major Westeros water cooler moment. It’s shocking. It’s brutal. And it has a cool nickname (though viewers who haven’t read the books might wonder what the heck it means).

The Season 2 premiere served up Blood and Cheese on a platter, but for those just catching up, it may be hard to be certain of what just happened. So what just happened?

Who are Blood and Cheese?

Blood (played by Sam C. Wilson) is a member of the City Watch, the security force that Daemon once headed up in King’s Landing. (Blood’s counterpart in the books is a former member who lost his post for killing a prostitute.) Cheese (Mark Stobbart) is a Red Keep rat catcher who enjoys snacking on dairy products as much as his quarry does. Blood and Cheese aren’t referred to as such in the Season 2 premiere. Anyway their true names are lost, according to the historians of “Fire and Blood,” the Martin book on which “House of the Dragon” is (mostly) based. In their spare time, these two like long walks through tunnels, loyal dogs, and murder-for-hire.

Were there signs this was coming?

Yes, plenty. Did you smell a rat in Season 1? The Red Keep wasn’t infested only with rodents. It was thick with clues, too. Each time a rat scurried around the Red Keep — visiting King Viserys (Paddy Considine), crashing a wedding, nibbling a dragon skull — it served as foreshadowing. The creatures give us a guided tour of the castle’s hidden passageways (as do, therefore, their exterminators) and a means of sneaking up on the royal family at its most vulnerable. See the rat lapping up blood at the wedding of young Rhaenyra (Milly Alcock) and Laenor (Theo Nate), one of the most heavy-handed bits of rodent symbolism since the end of “The Departed.”

How did the event differ in the show from the book?

“House of the Dragon” takes great pains to show that the Blacks (Team Rhaenyra) did not intend to murder a small child in their quest for vengeance; Aemond (Ewan Mitchell) was the intended target when Daemon (Matt Smith) secretly hired the assassins. That’s not the case in “Fire and Blood,” which depicts an attack that is much more strategic, brutal and devastating. How so? Picture Helaena (Phia Saban) being forced to make a “Sophie’s Choice” between two sons, the heir (Jaehaerys) and the spare (Maelor, not represented in the show). Or how about Blood and Cheese threatening to rape a little girl, taunting a little boy and killing some servants — all while Alicent (Olivia Cooke), bound and gagged, is made to watch.

Why is this event significant?

Nothing says the gloves are off like beheading a baby. (OK, toddler.) Even if the assassination of an innocent child with a weird thing for Small Council stones wasn’t the goal, there’s really no defending it, is there? It’s unnecessary. It’s cruel. It’s a violation of the rules of engagement. And now the tone is set for the conflict to come. An eye for an eye, a son for a son, and soon the world of Westeros will be blind with rage.