The neotropical frogLeptodactylusalbilabrisexhibits the greatest sensitivity to substrate‐borne vibrations (seismic stimuli) reported to date for any terrestrial animal. Nerve fibers from the source of this extraordinary sensitivity in the ear show clear stimulus‐evoked modulations of their resting discharge rates in response to sinusoidal seismic stimuli with peak accelerations less than 0.001 cm/s2(10−6g). Evidence indicates that its source is the saccule, an organ of hearing in fish and of balance in man. We report that single vibration‐sensitive fibers in the white‐lipped frog saturate at (whole animal) displacements of 10 Å peak to peak [Fig. 1(b)]. Assuming a conservative 20‐dB dynamic range for these fibers, theinvivofrog saccule and the mammalian cochlea exhibit roughly equal sensitivities to displacement.