Cinema popcorn and diet coke

We went to our local Vue cinema to see Pan's Labyryinth this afternoon. It was fantastic (go and see it) but be warned, when you leave the cinema you might feel very tense and a bit screwed up, like someone's stalking the streets out to get you or something. Anyway, in the cinema we shared a large diet coke, and some salted popcorn. We asked for medium but got given large - well, kind of extra large if you ask me, but that's how it came.

BTW - I always have salted, not sweet. Who on earth buys sweet popcorn? I don't think I know anyone who does. Also, why is the bottom third of the popcorn always inedible? At the bottom of the tub it's just the skin of the corn and unburst corns - surely they should fall to the bottom of the big containers? It seems like they allocate a certain amount of inedible popcorn to each person... hmmm.