If a guest's hunger need isn't met, then their happiness will greatly decrease. When a guest gets hungry, they'll go out to get food from a food stand. This can be changed simply by meeting the other needs of the guests. Guests all have five standards that need to be met: The first is happiness, which is simply a measure of how happy a guest is. The way to please guests is to meet their standards. This can be done in a plethora of ways, and can be very difficult to do.
In Zoo Tycoon, one of the goals is to keep guests happy.
