http://breezewiki.catsarchywsyuss6jdxlypsw5dc7owd5u5tr6bujxb7o6xw2hipqehyd.onion/minecraft/wiki/Infested_Block
If the player attacks a silverfish directly with a sword , bow , or potion of Harming , or when a silverfish takes poison damage, nearby infested blocks break, spawning more aggressive silverfish. If the silverfish is killed in one hit, then nearby infested blocks do not break, and no silverfish spawn from them.