In this case, you can just break off a corner and rub it out; no knife needed. It's ribbon pressed (a cake), not leaf pressed (a plug), so this works just fine. MSO is right about plugs though: they need to be cut with a knife. It's can be confusing since C&D makes both cakes and plugs, but most of the best-known ones are cakes: Pirate Kake, Blockade Runner, Black Frigate, Briar Fox, Bourbon Bleu etc etc
Sykes