I agree with Frogmeister. If they have a video recorder (juliet's little movie for jack) and they have the video monitors to different locations around the island - who knows what they could record and play back. Edit out the name Carl and play for Jack.

Just because Jack doesn't know juliet or alex's voice doesn't mean that he can't be a pawn in THEIR game. He doesn't have to recognize the voice. I DO think he would probably recognize juliet's voice by now. She's be hanging around him a lot.

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