The functional approach to comparative cognition research is exemplified by Shettleworth's (2010) book Cognition, Evolution, and Behavior. In this book, Shettleworth brings together the evolutionary perspective of behavioral ecology, the relative simplicity of behavior analysis, and the diverse research programs of cognitive psychology. This approach does not avoid the use of cognitive terminology but uses it to generate testable hypotheses that have the potential to provide evidence for or against the cognitive hypothesis. Unlike behavioral ecology and cognitive psychology, this approach postulates contingency learning as the default account of behavior but tests cognitive hypotheses against the default alternative. In this review, I present the results of three lines of research as examples of the kind of research that has been used to test cognitive hypotheses: functional equivalence, cognitive mapping, and rehearsal processes, all of which are covered by Shettleworth. In each case, I would argue that these experiments would not have been conducted had it not been for the hypothesis that a cognitive process might be involved. Whether or not evidence is found for the existence of a cognitive process, the results of such experiments are of interest for what they tell us about behavior as well as for their heuristic value.