I enjoyed this so very much! I love your characterizations of both Snape and Moody here, and the banter between the two was priceless.
Severus' waspish sense of humour shines through beautifully: "I suppose I am to conclude from that articulate and effective sales pitch that you wish me to purchase this. . .ancient horse blanket and a rag." - and I adore the way that he is very strongly committed to a.) ridding the world of Dark objects and b.) helping Moody convalesce (there's never a suggestion that he won't play nurse - which I think is very admirable of him).
The rhinoceros idea worked superbly - it's quite special to come across a new (and amusing!) plot device after several years of reading fanfic, and I bought this one hook, line and sinker. To that end, this exchange made me giggle in particular:
"Do you think I would have de-rhino'd for just any one?" Moody demanded, lifting his mug again and tossing back the rest of the tea in a single swallow.
"De-rhino'd?"
"Transfigured back into myself. Shuffled off the rhino coil, to borrow a phrase.
'De-rhino'd' is such a marvellous word! ;-)
Moody is a character I have seen written only a few times, and never as satisfyingly as you have here. I love the way you have counterbalanced his roughness and aggression with a very sane dedication to the Light, and some childish (rather sweet!) moments of humour and enjoyment (seeing him whizz objects across the room with glee was lovely). This line especially made me laugh: "Now that I've got my magic back," he said as he sat down, "I'm going to do something about the pitiful wards you've got on this place. They wouldn't keep a sodding kitten out." and also: But beyond muttering, "I feel like a bloody wanker," he raised no fuss as Snape tipped warm oil onto his back and began to smooth it in with deft strokes of his long fingers. - You've done a great job at making the characters sound properly British :-)
I like the give-and-take partnership you have built for them by the end, and as another reviewer notes above, I'd be very keen to read of their further adventures finding Dark objects together, were you to write a sequel. Brava all round!