What does the cobblestone monster egg do in minecraft?

the cobblestone monster egg is a lot different from regular cobblestone. first of all, when you break it, it breaks as quickly as sand. even with your fists. second of all, when you break it, a silverfish comes out and attacks you. if you don't know what a silverfish is its a little insect that usually lives in a stronghold, where end portals spawn. they hide in blocks and when you break them they attack you. if you hit them more of them hiding come out and attack you.