Damon: Kate is raising Claire's son, Aaron, as her own. She knows that Claire, who was Aaron's mother, is now gone, and the only way that she can protect Aaron is to say he is hers. And we later realize, emotionally, Kate's still reeling from Sawyer's decision to jump off the helicopter. This man that she really loved left her, abandoned her, decided to stay behind on the island. She's trying to heal the emotional scar left by Sawyer taking himself out of the equation.
Carlton: Our characters have these encounters with things that that took place in the island's past and none is any more significant than Sawyer wandering through the jungle and seeing Kate helping Claire give birth. This is an incredibly powerful, emotional moment for him.
Damon: Kate doesn't realize she's replacing the wound left by Sawyer with Aaron. Ironically it's pointed out to her by an ex-girlfriend of Sawyer.
Damon: Sawyer and Juliet get along great. There's none of the sort of emotional fireworks that existed between him and Kate. But now Kate's back, and as soon as they see each other that chemistry just locks in for both of them.
Carlton: And that throws a big wrench in the mechanism, doesn't it?