In a cage, a blue tree monitor (Varanus macraei) rests peacefully on a branch. All attention is drawn to its long, prehensile tail, which slowly coils and uncoils in an almost perfect spiral.

This tail, which represents nearly two-thirds of the animal’s length, is a veritable fifth limb. In the wild, it allows the monitor to grip branches, maintain its balance, and move through the trees of the forests on the Indonesian island of Batanta. Seen up close, this display of flexibility is particularly satisfying to watch.