Informal RLJ

Funny the first hint of it that you get is in AGOT:

"Lord Eddard has never taken any interest in anything that happened south of the Neck," the woman said. "Never. I tell you, he means to move against us. Why else would he leave the seat of his power?"
"A hundred reasons. Duty. Honor. He yearns to write his name large across the book of history, to get away from his wife, or both. Perhaps he just wants to be warm for once in his life."
"His wife is Lady Arryn's sister. It's a wonder Lysa was not here to greet us with her accusations."
Bran looked down. There was a narrow ledge beneath the window, only a few inches wide. He tried to lower himself toward it. Too far. He would never reach.
"You fret too much. Lysa Arryn is a frightened cow."
"That frightened cow shared Jon Arryn's bed."
"If she knew anything, she would have gone to Robert before she fled King's Landing."
"When he had already agreed to foster that weakling son of hers at Casterly Rock? I think not. She knew the boy's life would be hostage to her silence. She may grow bolder now that he's safe atop the Eyrie."
"Mothers." The man made the word sound like a curse. "I think birthing does something to your minds. You are all mad." He laughed. It was a bitter sound. "Let Lady Arryn grow as bold as she likes. Whatever she knows, whatever she thinks she knows, she has no proof." He paused a moment. "Or does she?"
"Do you think the king will require proof?" the woman said. "I tell you, he loves me not."
"And whose fault is that, sweet sister?"
Bran studied the ledge. He could drop down. It was too narrow to land on, but if he could catch hold as he fell past, pull himself up . . . except that might make a noise, draw them to the window. He was not sure what he was hearing, but he knew it was not meant for his ears.
"You are as blind as Robert," the woman was saying.
"If you mean I see the same thing, yes," the man said. "I see a man who would sooner die than betray his king."
"He betrayed one already, or have you forgotten?" the woman said. "Oh, I don't deny he's loyal to Robert, that's obvious. What happens when Robert dies and Joff takes the throne? And the sooner that comes to pass, the safer we'll all be.

Catelyn saw her face change. It was as if the sun had gone behind a cloud. "Have you taken leave of your senses?" Lysa snapped at her. "To bring him here, without a word of permission, without so much as a warning, to drag us into your quarrels with the Lannisters …"
"My quarrels?" Catelyn could scarce believe what she was hearing. A great fire burned in the hearth, but there was no trace of warmth in Lysa's voice. "They were your quarrels first, sister. It was you who sent me that cursed letter, you who wrote that the Lannisters had murdered your husband."

He wondered which of them had sent the footpad to silence the Stark boy, and whether they had truly conspired at the death of Lord Arryn. If the old Hand had been murdered, it was deftly and subtly done. Men of his age died of sudden illness all the time. In contrast, sending some oaf with a stolen knife after Brandon Stark struck him as unbelievably clumsy. And wasn't that peculiar, come to think on it . . .
Tyrion shivered. Now there was a nasty suspicion. Perhaps the direwolf and the lion were not the only beasts in the woods, and if that was true, someone was using him as a catspaw. Tyrion Lannister hated being used.

Ser Rodrik tugged at his whiskers. "Poison, well . . . that could be the dwarf's work, true enough. Or Cersei's. It's said poison is a woman's weapon, begging your pardons, my lady."

A more poetic easter egg, I think: Alyssa's Tears. Alyssa Arryn gets mentioned 7 times during Cat's visit, and has a remarkably similar name to Lysa Arryn. When Bronn defeats Lysa's champion, he knocks down the statue of Alyssa. Fairly obvious connection. The waterfall next to the Eyrie is known as Alyssa's Tears, and is described as a "ghost torrent", it's waters never reaching the ground, as Alyssa never cried for her dead family. We learn all this in the same chapter (40) where we get:






Agreed!