ZOMBIE runs in a multithreaded environment. Several entities may be animated at once, and each may perform multiple tasks at once. The relative speeds and orders in which the entities perform tasks is undefined, and should not be relied on by the programmer.
Entities and their tasks may be active or inactive. An active entity is one which has been animated, disturbed, or is free-willed. A zombie or ghost that has been summoned and bound is inactive. An active task is one that has been animated; an inactive task is one that has been bound, or that the entity has completed.
Ha! How much fun. I'll have to poke at this on some sunny day to see it work.