Minecraft wiki entry for Axolotl, associated text: If an axolotl takes damage underwater, it may play dead, dropping to the ground for 200 game ticks (10 seconds) while gaining Regeneration I. Hostile aquatic mobs ignore healing axolotls. There is a 1⁄3 chance for an axolotl to play dead to recover 4. In addition, if either a random integer from 0–2 (inclusive) is less than the amount of incoming damage, or the axolotl's health before the damage is dealt is less than 50% of its maximum health, it plays dead.