Soft coring: how to get a clarinet out of a flute?

As an everyday gesture, slicing can be frustrating in different ways. Cutting through a mozzarella ball with a dull blade will most certainly result in a poorly shaped slice, as the celebrated cheese will deform before it's cut, resulting in potentially disgraceful bites. Cutting occurs in a configuration so deformed as to give rise to a whole different shape once the process of cutting is achieved. We study the rich morphogenetics arising from such process through the example of coring: when a thin cylindrical metal tube is pushed into a soft elastomer, the extracted core is hour-glass shaped, reaching diameters far smaller than that of the coring tool. Assembling contributions from fracture mechanics, large deformation theory and friction, we build a simple yet quantitative understanding of the observed shapes and dynamometrics. Our study opens perspectives into complex programmable surface shaping, in a mundane, accessible setting fitted for an array of design applications.