*thinks about this* This is... quite a bit different to the situation where I'm from. In that case, it was suspected Voldemort's soul-shard had fled the vessel [Q] entirely because it had been reduced to ash. But... That's obviously not the case with you, since you're... *tries to say this diplomatically, but there isn't a way, really* ...still alive. In your case, what happened that caused it [the soul-shard] to vacate?
*expression remains polite, but his tone is impatient* I wasn't suggesting you would or should lift the stuff without asking. I was simply saying that it's not something anybody would sell to an underage wizard, and since that particular cactus isn't native to the UK, we couldn't collect the ingredient ourselves.
It's an important distinction. It's possible to fight something without being frightened of it, and the same the other way around. If you've studied werewolves at all, it explains why there is no injury to the individual on the transformation from human to wolf, but the return transformation leaves the individual with torn muscles and broken bones -- the human form knows not to resist the change, but the wolf form doesn't.
*deep breath, counts to ten, thinks of this as a sort of penance for everything he put his teachers through* It doesn't have to be a kitten. The important thing is that you manage to preserve the consciousness of the first shape after you've transformed the body into the second shape. It doesn't matter what anima- *stops, starts again* It does matter what animals you use, but only in the following way. You wouldn't Transfigure a bird into a kitten, for example, because the kitten might try to fly and that would be disastrous. Or same with the frog -- kitten into frog and not vice versa, otherwise you'll have a kitten that thinks it can swim, which again -- no.
Apart from that, it doesn't matter what animals you choose.