Head

Mob heads are decorative blocks. There are five variants of mob heads: Skeleton, Wither Skeleton, zombie, human and Creeper. The Wither Skeleton variant is a rare drop from the respective mob, with the other heads only available in Creative mode.

Uses
The main use of heads is for decoration. They can be oriented in 16 different directions on top of a block, and 4 directions on the sides of blocks, similar to signs. They cannot be placed on top of each other.

Wither skeleton skulls are essential for spawning a Wither. To do so, place 4 soul sand in a T-shape, then place three wither skeleton skulls on top. The orientation of the skulls does not matter.

Heads are also used in the crafting of Firework Stars. Firework Rockets crafted with said stars will have a creeper shaped explosion, regardless of which type of head was used.

The player can also wear heads as disguise, similarly to pumpkins. This will only replace the first layer of the player's skin. If the player has a second layer over their head, it will still render over the head. Occasionally, another mob may pick up a skull and wear it just as the player would. This is common when a wither skeleton drops a skull next to another mob in the nether. They can also be used as a decorative disguise, using dyed leather armor. Heads are not able to be pushed by pistons, as they have tile entities.

The only mobs which can wear the heads are the Skeleton, Wither Skeleton, Zombie, and Zombie Pigmen (Only the part that its skull shows). As of right now no other mobs can wear the heads. However, other mobs can wear heads using custom spawners via MCEdit.

As of 1.6, you may change the appearance of the head for it to have the same texture as a specific player's head, but this is only currently achievable through mods/external editors, by changing the NBT Tag of ExtraType to the player's username.

Trivia

 * When breaking any head, the particle effect of breaking it is the same as soul sand.
 * The most possible reason is because they don't have their own terrain.png spot or Blocks file, so a texture that made sense was chosen.
 * All heads are not to scale, but are, in fact, the same size (even though Wither Skeletons have larger heads than the other represented mobs).
 * Heads are one of the few blocks that do not use terrain.png (13w01b and earlier) or Textures/Blocks (13w02a and later) and take their textures from other objects.
 * Heads will break upon contact with water and lava.
 * The "hat layer" is not represented on mob heads.
 * Heads can be worn by zombies, skeletons, wither skeletons, and zombie pigmen.
 * In demo mode after the demo period has ended, breaking a Wither Skeleton skull will cause it to reappear as a normal skeleton skull.
 * Although Mob heads do not protect the player, an enchanted Mob head, when worn, will apply the said effects to the player.