Infested Block

Monster Egg (also known as Silverfish Block; called Silverfish Stone/Cobblestone/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, and are naturally found in strongholds and rarely in Extreme Hills biomes, hiding among the true blocks. When breaking it with a pickaxe it takes noticeably longer to mine than regular stone, cobblestone, or stone brick, making it relatively easy to distinguish from the regular blocks, if one is careful enough. The block can also be destroyed by hand fairly quickly, unlike regular stone blocks. Mining a Monster Egg with a Silk Touch enchantment does not give the player a Monster Egg block, but the type of block that the Monster Egg is disguised as.

Monster Eggs are meant to deceive players. When mined, it will spawn a Silverfish which will instantly attack the player. Also, if the player attacks a Silverfish directly with a sword, bow or potion of harming, nearby Monster Eggs will break, spawning other aggressive Silverfish. If the block is destroyed by an explosion (e.g., creepers, TNT, etc.), the Silverfish will die inside of the block, which gives no experience points. The Ender Dragon is also able to destroy Monster Eggs, and prevent a Silverfish from spawning. When a Silverfish is not pursuing the player, the Silverfish will go to the nearest stone, cobblestone, or stone brick and go inside it, converting the block into a Monster Egg. When mined, the spawned Silverfish will have full health.

Monster Eggs are available in the inventory in creative mode, and can also be made by placing a stone, cobblestone, or stone brick block, and right-clicking on it with a Silverfish spawn egg. The block will then convert into a Monster Egg. Attempting to add more Silverfish into the block will result in the silverfish spawning normally.