Kate insists that Claire needs to get to the caves so she can see Jack, but Claire denies that she's even having the baby. It's just gas pains, she says, and Kate's all, not even! Those are contractions! And they argue about it for a little while, but at any rate, Claire's not budging. So Kate starts yelling for help.
They're close enough to the beach for Jin to just barely hear her, but it's hard to make her out, what with his hammering and the waves crashing and the sound of his own shame and humiliation pounding in his ears. He listens a little more intently, determines that someone is indeed screaming for help, and tears off into the woods. He stops for a moment in one of those clearings that's big enough for the camera to spin around him and show off how good-looking he is (the Sydney Bristow cheekbone-chase-cam) for like five hours while he tries to determine where the yelling is coming from, and he takes off again.
The look of surprise on his face when he comes across Kate and Claire absolutely kills me, as does him saying "oh" or something that could easily be Korean for "oh, holy shit." Kate urgently tells him that he needs to get to the caves to get Jack, and fortunately she doesn't yell at him like Sawyer tends to. She says "Jack" enough times for Jin to say, "Jack! Doctor!" and Kate's all "ding ding ding!" She gives the backpack to Jin and tells him to hurry.
Back in the caves, Jack's saying, "Ask him again," to Sun, who reminds Jack that Boone is in shock. "That's why you need to ask him again," he says tiredly. Sun asks Boone what his blood type is, while Jack attempts, unsuccessfully, to prick his finger with a bamboo shoot. Sun isn't getting any answer from Boone other than "sputter gurgle death rattle," and she suggests to Jack that he use a smaller piece (to prick his finger). He spits out that veins are like "wet noodles," and he needs a needle that's sharp enough to pierce one but also hollow, and all he has is bamboo. Sun gives him a look like, "Don't look at me, I didn't crash the plane." Then Jack says it doesn't matter because of Boone's wounds, and they don't know his blood type anyway. Just then Boone sputters out something that sounds a lot like "A-negative." Jack and Sun both hear it, and Jack tells Sun to find Charlie and ask everybody what their blood type is. She runs off. "And find his sister," he calls after her. "Find Shannon."
At the moment, Shannon is traipsing through the jungle with Sayid leading. He's being all mysterious about where they're going, to such an extent that Shannon thinks he's actually Lost, or possibly just lost. He recognizes some trees, though. "It's this way, I think," he says, and keeps going. "Did you just say 'I think'?" asks Shannon, who nevertheless follows him. And it turns out another stretch of beach is right there. And Sayid has set up some sort of beach picnic. "Surprise," he says, and Shannon beams.
In the jungle, Jack is frustratedly throwing shit around when Charlie comes back. "I found an A," he tells Jack, who asks if it's positive or negative. "She doesn't know," says Charlie, who says he also found two B-positives and one AB-negative, "at least he thinks so," like, Charlie, this wasn't a bleedin' blood survey. Jack asks if he found any O-negative. "Sun said A-negative!" protests Charlie, which didn't seem to prevent him from finding out the other non-A-negative blood types, but whatever. Jack asks where Sun is, and Charlie says they split up, and he figured she'd be back here. "You only asked four people?" says Jack, and Charlie snaps that he asked the "whole sodding camp" but nobody knows their blood type. "I don't know my bloody blood type!" Oh, fine: heh. Sun shows up, and Jack asks if she found Shannon. Sun says no, that she was getting something for Jack, and she holds up a sea urchin. She plucks one of its spines, and tells him it's a hollow needle that's sharp enough to pierce a noodle. Jack's all impressed with Nurse MacGyver and says it's perfect. Then Charlie reminds him that they still need someone who's A-negative. Or O-negative, says Jack. "Right, which, judging by your tantrum, no one is," says Charlie. "Someone is," says Jack. Charlie deduces that Jack is, and starts spazzing, wondering why Jack made him ask everybody, and Jack quickly shuts him down by telling him that O-negative is universal donor. "It's in the ballpark, but it's not perfect," he says, adding that his blood could potentially send Boone into anaphylactic shock, stop his heart. "You mean he'll die?" says Charlie. Well, as we all learned from Itchy and Scratchy, you need a heart to live, so I'm going to assume that yes, Charlie, if his heart stops, he'll die. Everybody looks at each other all nervously, knowing full well that if the death is another fake-out, the audience is going to be pissed.