Great question (I like the new sig by the way)

I've seen the anatomy pics of deer before and witnessed the heated discussions you talk about. IMO the void is more than likely a 1 lung hit and an animal with a strog will to live. I don't see how it's possible to shoot under the spine and not catch at least 1 lung.(It dosen't take a huge hole to deflate a lung either)

Maybe we can write into myth busters and see if we can get a scientific answer.