I once fed a LIVE medium rat to my not fully grown male ball python, and he got scratched on the head by the rat claws. He still crushed the rat and and ate it, and his injured scales healed very quickly. I was probably pushing it with food size though. He killed the huge meals so easily though, and grew like a weed, so I kept doing it for a while, but now I stick to small rats, as he is full grown, and doesn't need any extra calories these days.