I couldn't get started on this, until I realised that "transubstantiation" had a literal meaning outside of Cathlic doctrine, and so...
SNAPE: Ah, there you are, Minerva. Are the Transfiguration classes going well this term?
McGONAGALL: Oh, yes, we have an excellent cohort this year; some real talent. And your Potions classes?
S: Ah, now, that's where I was leading.
M: Oh, come on, Severus, not this again.
S: Minerva, how precisely am I expected to instill young minds with the arcane rituals of elixirs and admixtures if you keep on telling them how to change stuff into other stuff. As soon as my back is turned they transfigurate a pile of ingredients into a completed potion, without even turning on the Bunsen burner. Where's the potioning in that, eh? Yesterday, some little Ravenclaw bastard didn't even bother going to the store room, they just waved the old wand and turned a One Direction pencil case into a vial of levitation serum.
M: And what's wrong with that?
S: It was my pencil case! And it's not doing it properly.
M: Surely, if the end result is the same, they have succeeded in applying their knowledge to the problem at hand. I'm very proud.
S: But it's cheating!
M: No, it's magic. Magic, as you may recall, consists of melding and shaping the forces of the natural world to your own whims. It is about short-circuiting the laws of creation. If I had to think of one word to describe magic, that word would be "cheating".
S: Well, it doesn't follow proper potions methodology.
M: Exactly. Because potions aren't actually magic. What you do doesn't really fall on the thaumaturgical spectrum, does it? Putting stuff in bottles in the right order isn't a trick, you know.
S: Is too!
M: And yet, don't you think it odd that every teacher in this school has a portrait of Merlin in their study, whereas you have a poster of Tom Cruise in Cocktail? Don't you think it telling that when I spent my gap year in the ice plains of the 7th dimension, you spent yours working in Boots. You're not a real wizard, Severus, deal with it.
S: How dare you!
M: Look, I'm sorry. I'm sorry you're crap at stuff, I'm sorry you never got off with Lily Evans, I'm sorry you look like Peter Beardsley's emaciated junkie cousin, and I'm sorry they put you in an office in what is basically the sewers, but you have to face up to the facts.
S: Right! You've done it now! I'm going to give you such a potioning. I'll potion you up so bad...just give me about 4 hours, an oven on gas mark 7 and a largish laboratory centrifuge and I'll -
[SFX: Poof!]
M: That's put paid to that! Ah, good morning, Professor Sprout.
SPROUT: Good morning, Minerva. Oh, has the staff room got a new chair?
M: Seems that way.
SPROUT: Oh. Looks a bit spindly. And why does the upholstery have a picture of One Direction?
