African snoutfishes and South American knifefishes communicate by weak, species-specific electric organ discharges (EODs) in the form of pulses or continuous waves. Both snoutfishes and knifefishes are highly sensitive to the waveform of EODs that, unlike ourselves for acoustical signals, trained fish discriminate even when identical in spectral composition. Field studies of close relatives in neighboring systems have advanced our understanding of ecology and evolution of snoutfishes and knifefishes and their electric sense.