Pursuit-deterrent signals - signals used by prey that apparently convince predators not to pursue them - were discovered 15 years ago, but their existence continues to rest on shaky empirical evidence. First, pursuit-deterrent signals are usually inferred by eliminating competing hypotheses rather than testing predictions derived from the pursuit-deterrent hypothesis directly. Second, the strength of selection pressures maintaining such signals in prey populations are unknown because behavioral ecologists infrequently observe natural predation attempts. Third, the nature of information passing between prey and predators is open to misinterpretation because measures are rarely taken to separate signals that advertise perception of the predator from those that advertise perception and the prey's condition.