The actions of a finite state machine can be broken up into internal and external actions. Separating the actions into the two categories makes it easier to define what our AI does in any given situation. The separation is helpful in the planning phase of creating AI, but it can also help in the scripting part as well, since you will know what will and will not be called by other classes and GameObjects. Another way this separation is beneficial is that it eases the work of multiple programmers working on the same AI; each programmer could work on separate parts of the AI without as many conflicts.
External actions are functions and activities that are activated when objects outside of the AI object act upon the AI object. Some examples of external actions include being hit by a player, having a spell being cast upon the player, falling from heights, losing the game by an external condition, communicating with external objects, and so on.
The external...