Just my humble opinion - I would think it would make the best sense to switch to rat fuzzies if they will take them, since eventually they will be better off on rats as they grow too large for mice... might as well switch them all earlier and not have to worry about switching later, when they might be more stuck in their ways... I've read some people's concerns that their snake wouldn't take a rat and instead would down several mice in a feeding. Personally, I'd like to avoid that if I possibly could!