Few fish from a school of Bigeye trevally (+Caranx sexfasciatus) break off to scratch themselves against the flank of a blacktip reef shark (Carcharhinus melanopterus). This is a common and world wide behaviour, with several species of jacks scratching themselves on sharks in this way. The sharks rarely seem to enjoy it. Misool, Raja Ampat, West Papua, Indonesia. Ceram Sea. Tropical West Pacific Ocean.