Killer whales have a formidable reputation as one of the ocean’s most ferocious predators. Hunting stealthily in packs, some populations pursue ocean-going mammals, however, other killer whales prefer to dine on a diet of fish alone, posing little or no threat to the mammals that share their waters. Knowing that some species, including birds and mammals, are capable of assessing the risk that they are under from predators in the vicinity, Matthew Bowers from Duke University and colleagues wondered whether aquatic mammals that are known to reside alongside killer whales and feature on their menu could distinguish the calls of the predatory killers from those of other marine mammals. With his Ph.D. supervisors, Douglas Nowacek and Andrew Read from Duke University, USA, and Ari Friedlander (University of California at Santa Cruz, USA), Vincent Janik (University of St Andrews, UK) and Brandon Southall (Southall Environmental Associates, USA), Bowers decided to investigate how pilot whales and Risso’s dolphins react to the calls of killer whales. They publish their discovery that a subset of orca calls—with many of the characteristics that are found in human screams—trigger whales and dolphins to flea, while other less threatening calls do not provoke cetaceans to take evasive action, in Journal of Experimental Biology.