Minecraft wiki entry for Music_disc_farming, associated text: Using trapdoors, it is possible to trick creepers into thinking that they can walk over a hole. This is because mobs see trapdoors as safe to walk on, even when open. In the example video below, a skeleton is trapped behind two trapdoors, while a creeper is lured in front of it using trapdoors. The player can then stand behind the creeper causing the skeleton to finish the job.