The technique, called percussive foraging, is known in only a handful of animals. The third finger is reduced almost to bone and used purely as a tapping probe. The ears are large, independently mobile and tuned to the frequency range that distinguishes solid wood from a tunnel beneath the surface.
The extraction finger is the fourth, longer and highly flexible, and unusual among primates in having a ball-and-socket joint at its base that allows it to rotate inside a narrow tunnel. 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.