Minecraft wiki entry for Achievement_guide, associated text: You need to deplete your hunger bar to zero(empty), then eat rotten flesh. Hunger bar can also be depleted by sprinting while jumping at only 2 blocks high, eating pufferfish also can deplete hunger much faster but is potentially too risky. Rotten flesh can be found in chests in some generated structures, by killing zombies and their variants, or by fishing. If you have a tamed cat which you leave standing while you sleep, the cat can also bring you a gift of rotten flesh.