The hippocampus is needed for at least one kind of trace classical conditioning, the air-puff eye-blink paradigm. A simple model of region CA3 predicts three basic, quantitative observations of the learning behavior of rabbits. One particular quantified prediction is the learnable trace interval. The boundary region of the reliably learnable trace interval represents a phase transition. Within this transition, three behaviorally distinguishable modes are expressed: failure to blink; blink too soon; and occasionally, appropriate predictive blinking. In the region of the phase transition, there is a small sub-interval where the behavioral modes fluctuate rapidly from trial to trial for individual simulations. Such observed fluctuations are an experimental prediction by the model. The discussion also includes a brief conjecture concerning the underlying cause of the phase transition and the fluctuations.