Bran Semi-Warged Catelyn

When Catelyn sat by Bran's bedside, she included herself in the life-link between Bran and Summer, to her detriment. Since the situation serves primarily as foreshadowing of Bran's abilities, it doesn't effect the story and is heavily disguised as Catelyn having been made a nervous wreck by worry for her child. It would be easy to discount it as that, except that Bran later wargs Hodor.

Catelyn's state of total fixation on Bran is suspicious

When Maester Luwin comes to ask her to look at the inventory and make appointments, she thinks Bran’s hair is getting long and she’ll need to cut it, wondering about moving Bran’s bed to the window for the morning light since he’s so pale. When Luwin still presses, Catelyn yells at him that the only thing she can care about is her dying son. When Robb sees the fire, Catelyn panics and asks him to help her to move Bran to safety. When Robb tells her it’s the library tower, she says “Thank the gods” and Robb looks at her like she’s gone mad.

Catelyn can't move because Bran is holding her hand

After he’s sent Luwin out, Robb says:

"Mother, I need you too. I'm trying but I can't...I can't do it all by myself." His voice broke with sudden emotion and Catelyn remembered that he was only fourteen. She wanted to get up and go to him, but Bran was still holding her hand and she could not move. - AGOT Catelyn III

When she tries to pull away from Bran, Summer begins to howl.

"I would swear that wolf of his is keeping the boy alive. The creature is outside his window day and night, howling. Every time they chase it away, it returns. The maester said they closed the window once, to shut out the noise, and Bran seemed to weaken. When they opened it again, his heart beat stronger." AGOT Tyrion I

Robb opens the window to better hear Summer and basks in the feeling, but Catelyn feels it in a way that is unusually extreme. She cries out repeatedly to make them stop, saying:

“...kill them all if you must, just make them stop!” -AGOT Catelyn III

She doesn’t know how she has wound up on the floor. She begs Rob to close the window. He says he will if she agrees to sleep, but Catelyn is terrified of waking to find Bran has died. She screams, covers her ears, and begs Robb to close the window.

Catelyn's fixation on Bran relinquishes when Summer enters the room

When her hand is wounded by the catspaw and Summer steals into the room to kill the man, Catelyn holds out her wounded hand to the wolf, thanking him. He licks her wound clean before joining Bran on his bed. Catelyn begins to laugh hysterically and lets herself be removed from the room. When she wakes, days later, feeling herself again, Catelyn decides she must go to King’s Landing and is so little concerned for Bran that Robb is baffled. “You can’t mean to leave him.” The change in Catelyn is supposed to be surprising, even if it’s only that she’s herself again.