Not only deer, but all antlery animals (moose, reindeer, elk, etc). It's completely normal and pain free, but it looks like something out of a horror movie.
For some reason, this does not happen to animals with horns, such as cows.
Not necessarily. I've seen failures like this if the boot partition works, but fails to mount the root partition. systemd then fails to proceed, and shuts down the running services.
I'm a hobbyist programmer myself. I've picked up a few languages along the way, and by far the best approach I have found to learning is a simple but real practical use case. Find the smallest task you want your program to do, break it down into even smaller subsections, and then start to figure out how to transform it into code. It usually takes less code and knowledge about a language than you think.