their digestion turns bone into salt and dust. finally nothing remains other than the sturdiest parts of teeth, and crap.

you need to worry if the width of the snake increases around one location of the body, most commonly if things get constipated it builds up above the cloaca. so you need to be on the watch and consult a vet if things go sour.

but then, the slow metabolism and their ability to digest bones and somehow condense it all allows for some crazy volume reduction. you need to track the overall body shape, that will go out of bounds if the BP is sick.

also pictures will help a lot.