I agree with Themostpotente - you win at Smutmas! holy fu-- I mean, that was fantastic. I love that you took it the whole way -- from rhyme to illustrations, to full book layout, it's so very well crafted. And Snape/Filch isn't my favorite pairing, but you've managed to portray it so well -- it works and there's more than just sex behind it. Major Kudos for getting subtle emotion into a verse like this, that's not an easy thing to do.
And just cause I have to say it, my favorite is the last page, and especially the last verse. Fantastic job all around!