He won't feel it initially, in the heat of battle. He might not even realize his arm is gone if he doesn't see it happen. But once he gets a chance to pay attention, he will feel it and it will hurt a lot. You can read the account by Bethany Hamilton in Soul Surfer of her getting her arm bitten off by a shark. I also read about someone who got her leg bitten off by a shark while she was being pulled onto a boat to escape the shark, and she just felt a *pop* and then was being pulled onto the boat and her leg wasn't there. There was also a detailed account of a guy who had his fingers, then his arm bitten off by a shark--Chuck Anderson. He didn't feel the shark take his fingers, and as he struggled to free his arm from the mouth of the shark, he didn't feel any pain. I'm just mentioning sharks because I've heard their stories, but don't know stories of people who lost limbs in other circumstances that involved a sudden, almost surgical loss, rather than a mauling.