Observed: Red-bellied piranha Pygocentrus nattereri
Drums: When circling another piranha for a fight, especially over food.
Snaps: Its jaws shut loudly when it tries to bite its prey or a foe. So says a study by researchers at the University of Liège in Belgium, the first to determine how the Amazonian freshwater fish makes sounds and what they signify. The barking and drumming come from an organ called the swim bladder; the snapping noise is done with a firm bite. The researchers studied piranha in a tank (and got their fingers nipped). Now they want to know whether piranha vocalize while mating.