A Bit o' Magic about Argus Filch and Mrs. Norris - the absolute canon version, I've decided. All the information you need to know is there, up in the header; just go read it. I don't have it in me to write up my own version of a rec-header at the moment.
In cased you missed it, that's A Bit O' Magic and you should go read it right now.
I feel the need to go drive to Providence and hug every cat in the household, especially three-legged old Foofy.