First, know if the rat you fed was actually a medium. This is done by weight. Second, just because a snake will eat something does not mean it should. Snakes (usually not ball pythons) can eat themselves to death. They can develop fatty liver disease. In my experience, ball pythons will not normally do this but many especially males will go on prolonged fasts to counter the overeating. My males never get anything larger than a small. My females 3000+ grams do not get anything larger than a medium. Even feeding like this most of my collection will fast for about two months of the year. It is your animal. Do as you please however remember on this board there are many people that have a roomful of animals with many years of experience. You can choose to follow it or not.