If you are Zerg and you have a Queen and you're able to use the abilaty "Spawn Broodlings", than use it on an enemy non-mechanical ground unit and when the two broodlings come out of that unit, hit one of the broodlings with "Spawn Broodlings", and two Broodlings will come out of that Broodling. If you do this reapeatedly than you can have an army of them.