Spoiler Warning
To answer the question at the end... they attacked me. I don't normally go around shooting possums. I tried to dodge the possums initially and when I couldn't I did try and scare them off by shooting 'in the air' but that didn't seem to work. I wonder if I just let them attack me if they'll just go away or if they'll kill me eventually. There didn't seem to be any way of telling how much health I had, or even if that was a thing. They do very clearly hit you though.
Overall, it was a pretty enjoyable little game, but trying to shame the player for something you seem to be forced on them is not a good look in my opinion.