Without such lubrication, the insertion of a penis into a vagina could be painful for both partners. (The corresponding sign of tumescence in males is the erection of the penis.

• 如果没有这种润滑，阴茎对阴道的插入能使两个性伴都产生疼痛。（在男性，膨胀的相应徵象是阴茎勃起。