Representative spectrograms from a microphone recording (airborne: top) and an accelerometer recording (substrate-borne: bottom) for a purring male that illustrates the broadband percussive sound present in many of our recordings. Percussive strikes (presumably with forelegs) appear as white vertical bars just before 1 second and at 2.5 seconds. The time is shown on the x-axis (seconds), and the colors (purple < red < orange < yellow < white) represent the power present at the various frequencies shown on the y-axis.