Quote Originally Posted by swansonbb View Post
That's unusual. Why don't you describe their enclosures or post pics?
How is that unusual? That is very common, actually. Ball pythons are easily stressed by such things. This is one of the many reasons we advise not to feed in separate enclosures.

To the OP, your ball shouldn't be on mice at 20 months of age. Most of us, myself included, start our balls on appropriately sized rats right out of the egg, although some of us favor hopper mice as their first couple meals. Underfeeding is a major issue in this hobby and one of my biggest pet peeves. Your snake should be eating 10-15% of its body weight every 5-7 days. As was suggested, get yourself a small digital scale and weigh your snake and its prey.