During the game, the AI agent must make decisions on which way to go, which are governed by rule-based policies. When the agent has to make a decision, she checks her rule list, starting with the rules with highest priority. In Ms. Pac-Man, ghost avoidance has the highest priority because ghosts will eat her. The next rule says that if there is an edible ghost on the board, then the agent should chase it, because eating ghosts results in the highest points.
One rule that the researchers found to be surprisingly effective was the rule that the agent should not turn back, if all directions are equally good. This rule prevents Ms. Pac-Man from traveling over paths where the dots have already been eaten, resulting in no points.”