The title of this episode, "What Is Dead May Never Die", is quoted from the Iron Islander's religious worship of the Drowned God. The Iron Islanders, called Ironborn, often use it as a war cry, or even as a formal greeting.
Tyrion Lannister: My sister wants to hurt me; she'll look for any weakness she can find. She can't know about you.
Shae: I'm the weakness?
Tyrion Lannister: It's a compliment, My Lady.
Shae: How is being a weakness a compliment?
Lord Varys: Power is a curious thing, my lord. Are you fond of riddles?
Tyrion Lannister: Why, am I about to hear one?
Lord Varys: Three great men sit in a room: a king, a prince, and a rich man. Between them stands a common sellsword. Each great man bids the sellsword kill the other two. Who lives? Who dies?
Tyrion Lannister: Depends on the sellsword.
Lord Varys: Does it? He has neither crown nor gold nor favor with the gods.
Tyrion Lannister: He has a sword, the power of life and death.
Lord Varys: But if it's swordsmen who rule, why do we pretend kings hold all the power? When Ned Stark lost his head, who was truly responsible? Joffrey? The executioner? Or something else?
Tyrion Lannister: I've decided I don't like riddles.
Lord Varys: Power resides where men believe it resides. It's a trick, a shadow on the wall. And a very small man can cast a very large shadow.
Shae: Every man who's tasted my cooking has told me what a good whore I am.