Ben needs to be aware of everything going on in the Lostie's camp. The Others have attempted to infiltrate the Losties for three seasons and it hasn't really worked for them. I think Ben is now trying to get a Lostie in his camp. He tried with Jack, but IMO, even though he's been acting strange this season, Jack still has no love for the Others. So now he's taking a stab at Locke.

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