Fig. 9. Acoustic and electromyogram traces from calls evoked by 90 ms trains of stimuli applied unilaterally to the sonic nerve. The sonic muscle is fast enough that stimulation at 50 Hz resulted in a series of separate twitches in which the entire two-part waveform of the produced sound can be seen. Action potentials matched stimulation frequencies to 360 Hz (not shown) but responded to alternate stimuli at 400 Hz.