I don't think it is possible for a deer to drown in it's own blood when shot through both lungs. As I understand biology, it is impossible to breath once both lungs have been compromised. Once both lungs have been punctured it is no longer able to maintain negative air pressure and the lungs cannot expand. The animal suffocates. I think the key is getting both lungs. The benefit of getting a lower shot is more blood on the ground rather than inside the cavity. Anyone feel free to correct my biology if I have it wrong but that is my understanding of how it works.