The probability distributions of bouts of licking and pauses between them in rats ingesting sucrose solutions were studied to determine if the durations of these ingestive and noningestive acts were controlled by a deterministic or probabilistic decision rule in the central nervous system. The duration of the bouts of licking could be modeled by a Poisson process, indicating that these bouts were terminated by a probabilistic rule. Three different types of pauses terminated the bouts of licking. Each averaged 0.3, 1.5, or 50-60 s in duration. The two longer pauses could be modeled by a Poisson process, indicating that their termination was also probabilistic in nature. The shorter pauses averaging 0.3 s could not and are more likely deterministically controlled.