Thanks for that post, I never knew a single lung hit on a deer could take 4 hours to do its job. I always thought a single lung would expire an animal in less than an hour.
There are some top experts who believe that a single lunged deer can actually survive. It is believed that deer have a membrane between the lungs which will not let the other lung collapse. Similar to humans and other animals. Dogs, however do not have the membrane and the second lung would collapse if the first is punctured. Again, I would suggest reading the above book, which goes into it in detail.