Suppose a group of skinchangers have the alternate form of wolves, and a pack of them attacked a magus
Would the magus have a bonus to his soak from Animal or Corpus?
If it was Corpus, would you
a) Tell them to use Corpus for a soak bonus rather than Animal, but not explain why, but let the players speculate?
b) Tell them to use Corpus rather than Animal and tell them this is out of character knowledge ?
c) Collect the soak information and do all the calculations yourself, and just tell them what level of wound they received.
d) Something else?
Corpus and animal: the best.
Corpus because of essential nature, Animal because of apparent nature.
d) For the sake of simplicity, I would check sheets at the start of the game, keeping the form bonus of the best art of each player , then substract it from damage, before asking the player his soak [without any form bonus = because my players do forget those!].
I simply would use Animal, because it is the animal form that is causing the damage.
We usually go with c), and not just when the Storyguide is trying to hide something (so that it's not obvious when it happens )
I am not usually storyguide and the only previous story I ran, the closest I came to a combat was the group trying to grab a bunch of mice, so it wouldn't be inconsistant for me to handle it that way. It is not how we normally do things though.
A transformed human is also affected by corpus, but it is primarily an animal. So I would use animal. It is a wolf (or whatever) after all. You can affect them with corpus, but they certainly affect ^you as animals.