The other thing to keep in mind is that the deer are moving while the arrow is moving through them. They are not a static target and it can make for some crazy shit too. Puncturing that diaphragm was crucial IMO. That makes it damn near impossible for them to breath and cuts down on their movement. It sucks for blood trails cause it allows the blood to pool in their guts, but it is just one more bit of trauma that helps recover them.