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Clown fish became famous thanks to the movie Finding Nemo. In real life, their social hierarchy is simple: larger fish dominate their smaller counterparts . Now we know that to reinforce this social structure, the fish communicate with aggressive and submissive audio signals.

Researchers recorded clown fish calls, capturing this noise as one chased a smaller fish. These popping sounds function as an aggression signal. When a clown fish has been chased and wishes to submit, it shakes its head in a submissive gesture and produces clicking noises like these. The researchers compared the aggressive and submissive calls, and found that the sound pulses in a submissive signal were shorter and more high-pitched.

Unlike many animals that use sound to draw in potential mates, clown fish appear to use their calls only as labels of social status. When a little fish makes submissive sounds to a larger one, neither has to invest in a physical confrontation. Which is good news for small-fry like Nemo.