He would assume that no one would travel that far alone with the Others lurking about. Anna told she would find the balloon if he drew the map and if it was there.

So...he just used the plural, no numbers, just more than one. He's talking to Jack and Locke, he's learned that they don't know about the map...they don't even know if anyone has gone to find the balloon.

I think Henry is just playing mind-games with them. Spread distrust through the Losties from within. If they're all divided in their loyalties, then it will be easy for Zeke and the Others to win.

Simple strategy, simple tactic. Like planting the mole in each group (the Losties and the Tailies) is a simple tactic.

Plus: They used different modes of attack on the two groups. Fear for the Tailies and just quiet spying on the Losties.

I think Zeke fears Jack and Locke more than he does Anna and Sayidd.

I also think Eko might have some connection with Dharma. His confession to Henry about the two Others that he killed ("I want you to know, it was a mistake"), might be a message to Henry that he (Eko) is another mole, and that would explain the disgusted look he gives Henry when Henry doesn't respond to his confession.

Does this sound plausible?

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charlie98210
"Whoa!" she said. "Cry 'Havoc!' And let loose the dogs of war!"
And, like Banquo's ghost, they just won't go away.