Infested Block

Monster Egg (also known as Silverfish Block; called Silverfish Stone, Silverfish Cobblestone, and Silverfish Stone Brick in Xbox 360 Edition) is a block that spawns silverfish when broken. Monster eggs have identical looks to either stone, cobblestone, or stone brick.

Obtaining
Monster eggs take the same amount of time to break with any tool. This makes monster eggs easier to distinguish from other blocks. When the block is broken, a silverfish spawns where it was broken.

Mining a Monster egg with a silk touch tool drops the block that the Monster Egg is disguised as, and does not spawn the silverfish.

If the block is destroyed by an explosion, the silverfish will die inside of the block, which gives no experience points.

Natural generation
Monster eggs are naturally found in strongholds and rarely in Extreme Hills biomes, among stone and stone brick blocks.

Creative
Monster eggs are available in the inventory in creative. They can also be made by placing a stone, cobblestone, or stone brick and then using a silverfish spawn egg on it. Attempting to add more Silverfish into the block will result in the silverfish spawning normally.

Usage
When mined, monster eggs will spawn a silverfish which will instantly attack the player. If the player attacks a silverfish directly with a sword, bow or potion of harming, or when a silverfish takes poison damage, nearby Monster Eggs will break, spawning other aggressive silverfish.

When a silverfish is not pursuing the player, the silverfish will go to the nearest stone, cobblestone, or stone brick and try to go inside it, converting the block into a monster egg. When mined, the spawned silverfish will have full health.

Trivia

 * If the Ender Dragon destroys a monster egg, no silverfish is spawned.

Silberfischchen-Stein Piedra con lepisma Bloc infesté Uovo di Mostro 怪物蛋