Interesting stuff about the MRI and scanning. The flashes of white light on Juliet were almost like flashbulbs going off (I know you don't use flashbulbs with MRI"S) as in taking pictures or scans. Juliet did not look directly at the white light, it almost seemed painful for her each time the light flashed. So if it is magnetic, does sonic "noise" interfere with that, scientifically I mean?
Props to Logan for finding that quote from Locke and Eko about Smokey.
The Ben-Others are aware of the Smoke monster, Juliet stated as much in the show when she said "we know very little about it." That shows that they know of it, but, like us, don't understand it... except that someone understands it scientifically enough to build that weird sonic fence (and distribute the pass code) to keep it out. Kind of like the swan station where someone knew enough to encase the "incident" in concrete (like Chernobyl, stated Sayid) and construct a countdown clock mechanism and a fail safe with key. Somebody knows more than they're saying.
Juliet's whole little act seemed very reminiscient of Ben's capture, but unlike Ben who never broke, Juliet blew it with the handcuff key and the sonic fence. Where there whispers during this epi? Does anyone know?

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`Dear, dear! How queer everything is to-day! And yesterday things went on just as usual. I wonder if I've been changed in the night? Let me think: was I the same when I got up this morning? I almost think I can remember feeling a little different. But if I'm not the same, the next question is, Who in the world am I? Ah, that's the great puzzle!'

-- Alice, from “Alice’s Adventure’s in Wonderland”