Lips are often viewed as a symbol for sensuality. This has many origins; above all that they are very sensitive as a tactile organ and feel pleasantly soft. It has been suggested that female lips are seen as sexually attractive because they mimic the appearance and sexual swelling of the labia of the vulva, and that the lips are therefore a secondary sex characteristic. Additionally, they are a part of the mouth and so are associated with its symbolic connections (see for example oral phase of the psychology according to Sigmund Freud).