Infested Block

Monster Egg (sometimes called Silverfish Block) is a block that may look like a Stone block, a Cobblestone block, or a Stone Brick block, but is actually a block that when destroyed will spawn a Silverfish. The block is easily destroyed by hand, distinguishing it from regular blocks. If you attack a Silverfish directly with a sword, a bow or a potion of harming, nearby Monster Eggs will break, spawning other aggressive Silverfish. Mining a Monster Egg with a Silk Touch enchantment gives the player the type of block that the Monster Egg was disguised as. As of snapshot 12w17a, the block is called "Stone Monster Egg", "Cobblestone Monster Egg", or "Stone Brick Monster Egg" depending on what kind of block it is. If the block is destroyed by an explosion from Creepers, TNT or fireballs from ghasts, the silverfish dies inside of the block, giving no experience points. The Ender Dragon can also destroy Monster Eggs, preventing a silverfish from spawning; it can only be destroyed by the player or when a silverfish near it takes damage from the player. Monster Eggs can be made in creative mode without cheats by placing a stone, cobblestone, or stone brick block, and right clicking on it with a silverfish spawn egg. The block will then contain one silverfish until broken. Attempting to add more silverfish into the block will result in the silverfish spawning normally. In order for the block to spawn silverfish naturally, it must be spawned in a Stronghold.