Minecraft wiki entry for Angerable, associated text:  AngerTime: Ticks until the mob becomes neutral. -2,147,483,648 to 0 for neutral mobs; 1 to 2,147,483,647 for angry mobs. Value depletes by one every tick if value is greater than 0. When the value turns from 1 to 0, the mob does not stop tracking the target until the target has exited the mob's detection radius. When hit by a player or when another mob of the same type within 32 blocks is hit by a player, the value is set to a random number between 400 and 800.
 AngryAt: The Universally Unique IDentifier of the entity that caused this mob to be angry, stored as four ints.