Minecraft wiki entry for Egg_farming, associated text: This system may be extended with a larger living area with all hoppers eventually pointing to one that goes to a chest. At a certain point, the system becomes prone to mob spawns, and slabs can be laid over hoppers to deter mobs spawning. (Hoppers can fetch dropped eggs through a slab.) As using many hoppers becomes too expensive, water flow is used instead of the initial collection in the following version.