To get the best out of mozzarella, rip it, don't slice it. Ripping allows the trapped coagulated fat in the cheese's protein chains (aka curds) to come apart organically by breaking into pieces on its own natural fault lines. The result is a more rustic and softer mozzarella with greater flavour absorbing capabilities. And its milky stringy-ness is much more pleasant to eat than a thick slice of mozzarella.  Use the hands, tear gently and enjoy the cheese in its natural glory.