This is the first time we get to see the 'monster' for a prolonged period rather than a brief glimpse as has been the case previously.

The 'monster' turns out to be black smoke.

Claire: And this is Aaron.
Eko: Aaron? Brother of Moses.
Claire: Yeah, that must've been tough to live up to, right?

Michael: Are you breaking in or breaking out?
Locke: I used to love those old silent movies where the robbers would crack a combination of the lock with their ear pressed up against the safe. And the money they stole was always in a white bag with a big dollar sign on it.
Michael: Silent movies, huh? You're not that old, man.
Locke: I'm old enough.

Tough Moroccan: It is true what they say about you.
Eko: And what is that?
Tough Moroccan: You have no soul.

Kate: You know you don't have to be belligerent just for belligerence's sake. Everyone loves you now.
Sawyer: Bull puckey.
Hurley: Yo, Sawyer. Glad you're back, man.
Sawyer: Yo yourself! Pillsbury!

Charlie: What if I don't? You gonna beat me with your Jesus stick? I find it a little odd that your scripture stick has dried blood on it.

The plane on the ground and the plane in the flashbacks DO NOT match. On the ground, the tail section has a small piece of writing on the side. In the flashbacks, it has a large number on the side: 57GWN6. We know that it's the same side because of the bloodstain Eko left on the inside. And the paint job on the outside hasn't been messed with. So what happened to the number?