Question of the week
What the hell is "the twist?"  Possibilities, in rough order of likelihood:

(1) Three tribe members each are swapped between Samburu and Boran.  (You are correct, sir!)
    Evidence:  The CBS web site tells us: "A SURVIVOR first! Every friendship and every alliance will be shattered."  Taking CBS promos at face value is a risky prospect, but from these words, we think the most likely scenario is that the AllRats and Elder alliances on Samburu are broken up, by switching two AllRats and either Frank or Teresa over to Boran, and having three Borans join Samburu.  This leaves each tribe evenly matched again, at least alliance-wise: three former Borans, two AllRats, and one Elder.  MB himself has described this as a minor change, and "something that will make you laugh," and Les Moonves called it a "curveball."  We think this situation best fits these descriptions, and it would make us laugh to see the AllRats all pissed off at having to hike to another camp.  There is precedent, as well: Survivor is based on the Swedish show Expedition Robinson, on which a tribe-member swap takes place.
     If this does happen, we think this helps us predict the bootees, especially in light of three other active prognostications: (A) "Diane's friends", (B) the Episode 6 title: "I'd Never Do It to You," and (C) Survivornews.net's spoiler that Lindsey was hospitalized in early August.  Teresa looks vulnerable under a switched-player scenario.  She will likely be the oldest woman, unless she ends up with MamaKim, and even then, MamaKim will have two loyal Borans on her side, while Teresa has only two marginally-allied AllRats.  Teresa is on Diane's list.  In episode 6, we foresee a situation in which Lindsey's so-called "dehydration" illness progresses to something sufficiently debilitating that she gets voted off - against her wishes, and breaking her trust with one of the other AllRats, who considers voting against her (this would have her exit July 28th, just in time to be in the hospital in early August, when she realizes she's not just tired).  The next week is the Merge, in which Samburu is down 4-6, and Silas gets picked off, not winning the first individual immunity.  At least, that's our story for now, and we'll probably change it several times before these weeks play out.
     We will note, however, that in an even 3-3 swap, the strategy at TC should be, like at an even merge, to figure out who has votes against them from the other tribe, and vote them off.  That spells trouble for Silas, Lindsey and Clarence.  We still think Ep.6 is about Silas and Lindsey, but they are both highly vulnerable in Ep.5 - perhaps the other two Samburus (maybe even Silas and Lindsey) convince Teresa to act like she has prior votes (as Colby did in S2), then another tie vote happens, with Teresa losing yet another tie-breaker trivia quiz?

(2) A merge of the two tribes into one campsite, where three mini-tribes of four are formed.
    The single campsite is required due to the sentry problems - you can't have everybody in one tiny tribe up all night, then expect them to compete in challenges.  The "three tribes" rumor first came from a New York Post article in the summer, and shortly thereafter was repeated by former Survivors Jeff Varner and Sean Keniff, perhaps after a few payments from MB himself to keep it circulating.  The most logical scenario would be to keep ICs tribal, have one tribe win immunity, and the two losers go to TC.  This would require three new tribe names, new sets of tribal colors and flags, and then they merge again in two weeks anyway.  Seems like a lot of effort to go to, and fairly confusing rules-wise, for a minimal strategy-thwarting gain.
    If this is actually "the twist," it will immediately endanger strong players, such as Silas, Lindsey and Clarence.  The best strategy for avoiding TC the next week is to get rid of the other losing tribe's strongest player. Since all three of them already have votes against, if they are distributed onto different tribes, one of them is toast.  Fitting in with the "Diane's Friends" theory, the next two to go should be Lindsey and Silas, in some order.  But we can't see a scenario in which Teresa would be vulnerable with three tribes, so we think that may be further evidence against this.

(3) A simple merge at twelve, as opposed to the the merge at ten in previous shows.
    This seems less likely, simply because it does nothing to break up alliances and friendships.  That would come only from defections, which is likely in the case of Frank and Teresa, but they are in no way allied or friendly with the rest of Samburu.  Nor does it do anything divisive to the Borans or the Mallrats.

Still-possible spoilers (in vague order)
(1) "Diane's friends" - list given by Diane in Final Chat of who she talks to from Samburu: "like Carl and Theresa [sic.], Linda, Lindsey and Silas."  Sounded fake at the time, but Carl's and Linda's boots are making this look better and better.  The importance here is that we think the non-jury members were sequestered from those bootees on the jury.  Based on the number of Samburus here, who Diane had never met beforehand, this would require every one of these people to be the next ones booted.  Linda's boot shows that the order was not exact, although for several reasons, we think it's roughly accurate, suggesting Teresa's next.
(2) "Carl's non-friend" (new!) - in Carl's Final Chat, he mentions he never really got to know KimP.  This would fit with the "Diane's list" of pre-jury bootees, all of whom presumably joined in on Diane's month-long safari as they were booted.
X(3) "Carl's Women," Carl also mentioned that he went on safari "surrounded by beautiful women."  This suggests Silas is not the next one to go.  (Guess we can't trust Carl).
X(4) "The Blue Tribe" (Teresa, KimP, Lindsey, Lex - based on blue photos in opening credits), which goes hand in hand with...
X(5) "The Twist" in Ep.5 putatively being a merge/redistribution into three tribes - splintering the AllRats.  The "Blue Tribe" theory only helps if there are three tribes, really.  Alternatively, the three Samburu women may be randomly selected to go over to Boran, while Lex and two (non-blue) Borans join Samburu. (Bad week for "spoiler" theories).