Wow, that is so cool!
When I was a kid, I stopped on the side of the road and picked up a dead possum and tried to tan the skin with oak leaves. (Maybe I was a little weird... haha!)
It started working but I think I did not clean the skin well enough so it was blotchy looking, and eventually my mom made me throw it out because she was tired of it being around and grossing her out. Haven't tried tanning anything since, but it would be a cool skill to have.