The Cysteine from hair thing does not appear to be well supported by evidence. I won’t say it doesn’t happen, but I don’t think the phenomenon is nearly as prevalent as its internet mentions would suggest.
Regarding the castoreum - I just checked alibaba, and that stuff is at least $2 per gram - that’s roughly a hundred times more expensive than buying vanilla beans on the same website. You’re going to have to buy some ridiculously expensive boutique ice cream if you want to taste beaver butt.
