Thanks to Hollywood, piranhas have a bad reputation and it would be a brave scientist that chose to plunge their hand into a tank full of them. But that didn’t deter Sandie Millot, Pierre Vandewalle and Eric Parmentier from the University of Liège, Belgium. ‘You just have to pick them up and they make sounds,’ says Parmentier. However, it wasn’t clear when and why piranhas produce sounds naturally. Intrigued by fish acoustic communication and the mechanisms that they use to generate sound, the team monitored the behaviour of small groups of captive red-bellied piranhas to find out more about the curious sound (p. 3613).