Thanks to Survivor Fever, we now know that there is a switch in episode 5:
Announcer: Wednesday, it's a game changer.
Jeff Probst: Drop your buffs.
Announcer: Three tribes become two.
Sierra <camera confessional>: My old tribe is absolutely dead to me.
I heard Jim Nantz reading the following promo during the NCAA basketball game: "The Blue, White and No Collar tribes turn on each other and then disaster strikes."
I wonder if disaster only means Kelly's injury or is there more?
I'd say that Sierra looks like a very viable candidate for the episode 5 vote.