I've posted this before, but it got a lacklustre commentary so I thought I'd post it again:
Sayid's torture in "What Kate Does" brought back memories of Season 2 when Walt said that the Others were conducting "tests" on Walt. Could it be that these tests were to discover if he was infected by the darkness too? Since Walt was appearing in places he shouldn't have been, it could be that he was infected by whatever has claimed Sayid and Claire, and perhaps his scale tipped in the balance of evil. At least, this is what the Others suspected. Share your thoughts.