Percussive foraging combines three specialisations. The third finger is elongated, hairless and unusually thin, and its joint allows it to swing more freely than a normal digit. The ears are large and independently mobile, and the auditory system is tuned to the frequencies produced by tapping wood. The incisors grow continuously, like a rodent's, and are used to chisel a hole once a cavity is located.
The fourth finger, slightly longer, does much of the extraction once the hole is open. The animal also uses the technique on hard-shelled seeds and on ramy nuts, where the same gnaw-and-hook sequence applies. In the ecological role it occupies, breaking into wood for insect larvae, the aye-aye takes work done elsewhere by woodpeckers, which are absent from Madagascar.
Whether the aye-aye is genuinely echolocating, actively interpreting returned sound, or simply listening for larvae disturbed by the vibration, is not fully settled, though experiments favour an interpretation of cavity structure from the tap.