I don't think I've ever had a ball python refuse a live mouse. Ever... Well, maybe the first few times after hatching, but then again if they refuse mice, they won't touch rats either... Mice are invariably the first meal all of my babies eat and they'll never refuse another one. Yes, rats are much more efficient at putting weight on your snakes, and they are more economical. It's much easier to feed one rat to an adult ball python then to feed it 4 adult mice in order to make the same weight, but for some reason they just LOVE mice. Mice are like candy to ball pythons...