Palatability and reward... okay. A chocolate bar tastes good, so it's palatable. If it takes five pounds of chocolate to satisfy you (high sugar hershey's bar...), then it's low-reward. If a couple ounces satisfies (85 percent dark chocolate), then it's high reward. Took me a while to grok that. With the chocolate bar... if it's the cocoa-fix that you're looking for, you can see how dark chocolate would be more rewarding.