The technique, called percussive foraging, is known in only a handful of animals. The third finger is reduced almost to bone and serves as both the tapping probe and, after the wood is opened, the extraction hook. The ears are large, independently mobile and tuned to the frequency range that distinguishes solid wood from a tunnel beneath the surface.
That slender third digit is unusual among primates in having a ball-and-socket joint where it meets the palm, letting it swivel inside a narrow tunnel. The fourth finger is the longest and more robust, and observations of free-ranging aye-ayes show it taking a different set of jobs: grooming, gripping, and handling large soft fruit. The incisors grow continuously and self-sharpen against each other, an arrangement otherwise typical of rodents and the reason for the aye-aye's early misclassification.
Anatomical work published in 2019 described a small pseudothumb on the wrist, a cartilage and bone structure with its own musculature, apparently compensating for fingers so specialised that ordinary gripping became difficult.