Minecraft wiki entry for Mule, associated text: A mule's health ranges from 15–30, but tends toward the average of 22–23. Displayed hearts are health, divided by two, rounded down. A mule with a non-even number of health points (15, 17, 19, etc.) does not show the last half-heart. If the mule has lost one fewer health point than the inflicted damage and did not regenerate, it has an odd number of health points, otherwise, it has an even number of health points.