Please don't read any further if you don't want the season premiere spoiled for you.
Okay, so when I watched the season premiere on its first airing, in the scene where Shannon bumps into Walt, two things bothered me about what he says. One, I really had no idea what he said. Two, his lines are COMPLETELY out of sync with his lips.
So, being the resourceful person that I am, I decided to investigate. I got the episode digitized on my computer so that I could watch it over and over. I think I figured out what he was saying. It sounds like, "I have seen no one. No one's here." HOWEVER, having listened to it a few times, I noticed that there was something else about the way he said it. It had the familiar audio artifacts of sound that has been played in reverse. Hmmm!
So I fired up Windows Sound Recorder and had it capture the 3 seconds of Walt's dialogue. I reversed it and increased the volume by 25%, and I'll be damned, he IS saying something in reverse! Unfortunately, I'm still not positive as to what he's saying. It sounds like he says, "Where's the wood?" and then something else after that I can't decipher.
Maybe you guys will have better luck figuring it out. I posted the .wav file here. Any thoughts?
Good call. After reading Roy's interpretation and thinking about it for a bit I realized it probably had to something to do with some button in Desmond's underground lair. Remember when Walt first saw the hatch and how he freaked out? I'd bet this mystery button (perhaps the "EXECUTE" button that the camera lingered on during this episode?) is somewhere amongst Desmond's toys.