I asked nicely. [ Did you expect an actual answer, Childermass? Because canon is vague and so is Strange. He can't help but give him a wry little smile, a sort of 'I am being a shit and I know it' kind of a smile. ] We had a trade. Her desire for mine. Her desire was to become a cat, mine was to become mad.

[ There's no answer on the tonic. It isn't here, but a small little petty part of Strange wants to make Childermass worry. After all, it is a bit fun. And besides, madness (or eventually the appearance of madness) might have it's uses. Best to keep this one close to the chest. ]