Was the body cavity full of water? I was with a buddy who shot a bull a few years back and we had a similar story....he was out of arrows, bull was wedged in a log jam and couldn't get up. One arrow was racked up against the jam in some debris, but we couldn't grab it because the bull thrashed his head...long wait for him to die. I think he filled up with water and suffocated finally. I vowed never to bow hunt...that last only a couple years. Nice bull.