biologists have the worst attitude to acronyms
in this paper we describe a novel phenomena in primates wherein a male primate inserts his penis (P) into the mouth (O) of a willing conspecific (Wc) typically but not necessarily female. We characterise several observed instances of PO insertion (POI) and formulate hypotheses to elucidate the adaptive nature of WcPOI behaviour which we call “cocksucking” (CS)