I've seen quite a few porcupines laying like that. It was often a few seconds after noticing them & pulling the trigger. Destructive little bastards - they like to eat brake lines & other lines under a car; they love to chew apart plywood to get to whatever type of salt is contained in the glue. My father-in-law said, "don't shoot them, a lot of lives have been saved by porcupines." (You can run them down, kill them with a big stick, skin them easily, and their quills make an excellent fire starter; the rest = food.) After a porcupine destroyed his well shed, and destroyed several lines under his RV, it's open season on them.