To prevent suffocation, a furtum has a thick, cartilage backed barrier of tissue between the respiratory system and the digestive system that expands with the lungs, protecting both tracheas (complex story there, related to keeping air in the chamber) and the rest of the system from being crushed. Furthermore, for particularly wide objects or large occupants, Rose can spread her limbs out to allow for further spreading of the ribs (which themselves are separated and can split like a snake's)- or even in cases where the object will not fit past the rib cage comfortably, the esophagus and stomach can slip through the gap to be completely unhindered.

Rose is a giant fluffy friend inside and out and very clever, but she forgets about size dimensions, lol