Wow, that was really something! It left me dizzy, a little disoriented, and completely in love with Snape...kind of the way I imagine Harry feels at the end. Your language was beautiful--foaling horse? cluthing a letter like a moth by the wing? a button that wobbles like a loose tooth? I mean, amazing! :D And the stark pairing of Azkaban/Dementors/liquid depressant with those brilliant flashes of hilarity (MBNA family! Snape's collection of wigs! don't touch my orange!) was perfect. I loved the relatively quiet characterization of Snape and the kind of off-kilter, not-especially-bright Harry. Your dialogue, too, flowed with a natural rhythm--that is to say, often without any at all. It so realistic though. I'm thinking creme fraiche. Snape's concordance, with his descriptions of the figures, and his empiricism, and his matter of factness all around--it all fit together so wonderfully. I totally laughed at the Accio two lunches. Can they do that?? I mean, the poor oil riggers! :D I can just picture Harry's look of delight (tempered by the depressant, of course) when he discovers his scotch egg.
Dumbledore's remark about Severus not being a man of keys and the bird at the end wrap it up well enough for me, though I admit I wouldn't be averse to seeing Harry in Iceland. :) But really, this is perfect--a gorgeously textured response to the prompt!