1 more question (spoilers, if you're lucky enough not to have seen this)

I've just wasted an hour and a half of my life watching this film, and I've been left with several questions. Most of these have been discussed elsewhere on this board, but the thing that is bothering me the most concerns the part where Elisha Cuthbert's character is trapped in the glass box filling with sand.

Basically, I want to know where the sand comes from. There's a bloody lot of it (I'd have put her in a smaller box) and it's falling from above but when the bloke busts in from the top there's no sign of any pipes or tubes or a big vat think that the sand might come out of. Have I missed something, or is it just (more) poor film making?

Thanks.