Here is J.Wood's take on Cabin Fever
What if Keamy had a sibling? What if Keamy killed that sibling?
There's some reason to consider this, but it'll first take some working through "Cabin Fever" and the multitude of narrative and mythical mirror-twinned and paralleled coordinates. Every now and then an episode like "Cabin Fever" helps the audience (and probably the writers) get a snapshot of just where and how these coordinates are related, and they're so prevalent in this episode, this piece could almost be written in two columns to map out the conjunctions.
Start at the macro level, with the overall shape of the narrative. The first three seasons went through the Lostaways first encounters with the Others; their first encounters with the Tailies and the DHARMA Initiative; and the Survivors clash with the Others. The end of the third season seemed to be some kind of hinge where the second half of the narrative — the next three seasons — reflexes back upon the first three seasons. That means some of those original coordinates will be revisited, but since we're working back, not in the same way. Now we're seeing role-reversals and narrative mirror-twinning that expands beyond characters into groups, scenes, themes, and even structure (flashbacks and flashforwards).