Here, dark-coloured false killer whales (Pseudorca creassidens) are seen swimming alongside a group of paler-coloured bottlenose dolphins. Richard Robinson/Nature Picture Library/AlamySecret underwater messages can be disguised as clicks and whistles from whale or dolphin calls to fool eavesdroppers into believing they are hearing marine mammals.Because marine mammal sounds can interfere with military sonar systems, they are often deemed ocean noises and filtered out. These signals are a secretive way to communicate underwater.Chunyue and her colleagues from Tianjin University in China devised a test method to validate the idea.
