Think of it like changing the shape of a square so that it fits through a circular hole. Through some of their experiments, they're attempting to see if they can find a way to send us home if they Shift us enough. Supposedly, they're sometimes successful.

[Here he spreads his hands, looking back towards the village.] I don't know what they do to determine all of this, but I can't argue that they're learning nothing. I first came here nearly three years ago, and since then the population has been reduced by at least one hundred bodies.

[Not that he's grateful for what he's suffered through for it, but if he's to take what Bil said for truth, they were even responsible for sending him home four months ago.]