This is a photograph of the right paw print of a Bioko drill (Mandrillus leucophaeus poensis) taken during primate census at the Gran Caldera, Bioko Island, Equatorial Guinea.

Bushmeat hunting for drills and their consequent evasion of humans means the endangered, baboon-like drills are seldom seen in the wild, and even more rarely photographed. Instead, ephemeral evidence such as this damp, hand-like paw print – left just a minute or two before it was photographed – is the only trace of a near encounter between photographer and primate. The photograph begs the question “who is watching whom?”