Zombie Pigmen given a mob head to wear will show a glitchy texture where the mob head and Zombie Pigman head texture collide.

Steps to Reproduce:
1. Make a new Creative world.
2. Spawn a group of Zombie Pigmen.
3. Get any one of the five mob heads from the Creative inventory.
4. Drop the head until one of the Zombie Pigmen pick it up
5. Look at the top of the Pigman's head and notice the glitchy overlapping texture.