Mechanical cutting of visco-elastic polymers is experimentally investigated using sharp knives. The knife is aligned orthogonally to the substrate's surface, and is forced into the substrate. Two cutting scenarios are investigated i) plunge cutting, where the knife edge moves directly into the substrate, and ii) slicing, where the knife shears tangentially as it moves into the substrate. For slicing fracture lines emanating from the cut are observed, and the threshold forces for cutting are considerably smaller, indicating that the two cutting processes are very different.