"If you open both holes and turn the can upside down such that both holes are flooded, then one the scheme of one letting air in and one letting fluid out falls apart."
I disagree. The can isn't turned upside down and NEITHER is the deer. You can contort what I wrote all you want, but thats the plain truth of it. As for needing one hole higher than the other to let air in one and blood out the other, why would one have to be higher? And why do you assume that the blood would have to know which hole to flow out of? When you have two holes the vast majority of your bleeding comes from the exit wound. You have a slug punching a hole through the animal at a high rate of speed. You also have outside air rushing in the first hole opened (the entry wound) and all this combines to cause the blood to flow out the opposite hole. This is pretty much common sense stuff to anyone who's ever skinned out a deer with entry and exit holes. And the phrase I used about one hole to let cold air in and the other to let blood out, I did not coin the phrase. It is Elmer Keith's phrase and I imagine he killed more big game in his life than all of us combined.
Right, the can isn't turned upside down and neither is the deer. However, the way that a gas can works is by pressure equalization of the
poured liquid from an enclosed system. One hole is below the level of the fluid in the can and one hole is above the fluid during pouring.
So when you shoot a deer, which hole is below the blood level and when hole is above the blood level in the deer? Both are below. So the pour example doesn't really work for deer. You don't have one hole below the top level of the blood and another hole above than in an air cavity of the deer such that the hole in the air cavity will draw in air as gravity drains the blood from the hole below.
When you shoot a deer and get total penetration, then you have two holes that are both below the level of blood in the body, just like turning a gas can completely upside down. You don't get any
pour effect as you would get with pouring gas from a gas can.
When you shoot a closed full container such as a gas can (with water, not gas inside) and have the shot passes all the way through where both holes are below the level of the fluid, does one hole let air in and one hole fluid out as you claim? Nope, and it doesn't work that way on a deer either. Both holes will try to let air in and let fluid out at the same time.
You are right, this is fairly common sense stuff.
Elmer Keith might have claimed that one hole lets blood out and one hole lets air in, but if that is the case Elmer Keith didn't understand fluid dynamics and pressure equalization.