Not Constricting? Trying to get out? And other questions...

The issue with switching between rats and mice is not that your snake will not take both now. The issue is that it may not ALWAYS take both. There is a good chance that you may not experience many refusals, and there is also a good chance you will.

The reason most owners stick with one type of prey is because bp's do well with consistency. They don't do well (in captivity) with frequent changes to their diet or surroundings. If you want scientific facts behind that, well I can't give you any. I can only provide you with the tried and true methods of success and let you decide which route you will take as a new owner.