I think it's talking about food (dead animal) swimming in your stomach (body) and you go for a run to burn the calories.
I just don't know what the mailbox was about.
There seems to be a lot of discussion about what this work is or isn't. And, it is great to have this discussion. To start, it's categorized properly. If you aren't sure what transgressive poetry is, this is an example.
It's important to remember that there are many artists we tout as genius' today that were thought to be making a muddled mess in their time. Artists see the world in a new way first and express it. Then, science follows. Then, the rest of the world (kicking and screaming, but eventually). When confronted with a work that irks you or confounds you ~ look deeper. You will either find why it bothers you and this will only help your own work. Or, you will find why it confounds you and it will help you in living your life more fully.
It's not the work that is the issue. It is the observer. And, every work of art needs you to pull your weight when viewing or reading it. It's not a one-sided discussion. Questions are posed. It is your job as the viewer/reader to hear them and then to ponder them.
You can still hate the work. But, for fucks sake, try to find something beyond the nearest rock to throw at what doesn't please your senses straightaway.
Art should be disturbing and difficult whenever possible. And, this work is definitely pushing a lot of buttons for some reason. I hope those who feel their buttons being pushed dive a bit deeper and figure out why. Because that will be truly interesting to see expressed.