Infested Block

Monster Egg (also known as Silverfish Block or Block 97) is a block that spawn Silverfish when broken. Monster Eggs have identical looks to either Stone, Cobblestone, or Stone Brick, and are naturally found in Strongholds, hiding among the true blocks. The block can be easily destroyed by hand, distinguishing it from the blocks. Mining a Monster Egg with a Silk Touch enchantment gives the player 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 (ex. Creepers, TNT, fire charges, etc.), the Silverfish will die inside of the block, which gives no experience points. Ender Dragons are also able to destroy Monster Eggs, preventing 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 as of Snapshot 12w21b, 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.

Currently, the block is labeled as "Block 97", but as of Snapshot 12w17a, the block is labeled as "Stone Monster Egg", "Cobblestone Monster Egg", or "Stone Brick Monster Egg" depending on what kind of block it is.