Nocturnal Aye Aye lemurs are famous for their thin, spidery middle fingers, which they use to detect hidden prey like beetle grubs. The finger is packed with sensitive nerve endings so it uses a lot of energy, and, like any delicate device, it is best turned off when not in use.

This thermal image shows substantial temperature differences in a Duke Lemur Center Aye Aye’s right middle finger (near its nose), which is warming to probe a treat it has been offered, whereas the left middle finger (at lower right) is quite cool in its passive position.

Image courtesy of Nate Dominy and Gillian Moritz, Dartmouth College