When they surface again, Kate manages to call Sawyer "disgusting" just before asking for his help getting the briefcase. He calls her on her hypocrisy, but she says it's actually her case. So down they go again (Kate futilely tugs at the case, and needs Sawyer to yank it out), all the better for more chest shots of Sawyer and leg shots of Kate.
They surface one more time, and Sawyer hands the case to Kate, jokingly asking if she happens to have her key on her. Then he watches as she examines the case closely. If she's checking the sides and bottom for any other reason than for Sawyer to deduce that case isn't actually hers, I haven't figured it out. She admits that it's not. "Well, you wouldn't mind if I just take it?" he says. "I don't care," says Kate as nonchalantly as she can, which isn't very. Sawyer asks if there's anything she wants to tell him about the case. "Take it," she tells him, and strolls away.
Now we're back on the beach, where the waves have apparently given some viewers shivers in light of the disaster in southeast Asia, like, yeah, giant tsunamis that swept away villages and killed 150,000 versus the tide coming in and getting people's stuff wet on a television show on ABC, I can UNDERSTAND THE CONFUSION HERE, and as everyone hustles to move stuff out of the water's path, Sayid explains for our benefit that it isn't normal how quickly the tide has shifted, and Jack points out that there's a lot that's normal around this place, the fuselage will be underwater in days if this keeps up, and he suggests that the rest of the survivors move inland, which Sayid says people are reluctant to do (other than Kate, I guess).
So then they start talking about Rousseau, and Jack wants Sayid to take him there, but Sayid doesn't think that's a good idea, for whatever reason. Jack says Rousseau said there were others on the island, but Sayid says that Rousseau's mind is gone, and anyway maybe the wind was playing tricks on his ears, and none of this sounds like a good enough reason not to go back to the person who may know something about the people who kidnapped Claire, but WHATEVER, JACK, and WHATEVER, SAYID, and Jack asks about the maps and documents and what-have-you that Sayid got from Rousseau. Sayid says he's skilled in mathematics and decryptions, but these equations are unlike anything he's ever seen. There are French notations, and if Sayid were able to translate he might be able to make sense of the equations. Hmmm, if only someone around here could translate French, hey, Sayid? Someone who has already once TRANSLATED ROUSSEAU'S WORDS FOR YOU, SAYID? But his problem seems to be that "some things are better left untranslated." Jack's all, "Try telling that to him," as he points at Charlie, who's sitting all by himself, staring dejectedly into space. The best reason to figure out this whole Rousseau thing is Charlie's friendship with Claire, apparently, and not Claire's (and her baby's) well-being, or possibly getting off the island.