Knives. So we don't have to hit our brownies with bones.
It's very possible that, somewhere in the universe, some intelligent civilization might not have evolved knives. It's not a given, you know. Our species got lucky and discovered them early, but maybe there's some alien society that developed the wheel first, and so they just run over their food until it liquefies, and then they drink it down like a protein shake. Be thankful you're on a knife-centric planet.