The social drive becomes a need for people, the stimulation drive seeks toys and other objects, and the fatigue drive creates a need for sleep. When unattended, the drives move into an understimulated regime, so needs grow for social interaction and stimulation. Too much activity and the drives drift into the overstimulated regime, and a need grows for a break from the action. Kismet's emotions are not linear. The emotions break down into high and low values, positive and negative states, open or closed positions, each conforming to research on actual human emotions.
Happiness is near the center of the homeostatic regime, a state to which the robot aspires.
The expression of interest is also within the homeostatic regime. Calm is there too. Depending on sensory information flowing in through Kismet's eyes and the status of its motivational system, strategies form that activate behavior. For Kismet, the process of maintaining drives in the homeostatic regime is never-ending. Kismet even has a strategy for self-protection.