The tip, blade, or underside of the tongue may be used, and so might the nose, chin, teeth and lips. People give various reasons for their dislike or reluctance to perform cunnilingus, or having cunnilingus performed on them. The tongue can be inserted into the vagina , either stiffened or moving. But the Taoist ideal is not just about the male being enriched by female secretions; the female also benefits from her communion with the male, a feature that has led the sinologist , Kristofer Schipper, to denounce the ancient handbooks on the "Art of the Bedroom" as embracing a "kind of glorified male vampirism" that is not truly Taoist at all. It is believed that this is due to the transmission of HPV, a virus that has been implicated in the majority of cervical cancers and which has been detected in throat cancer tissue in numerous studies. The female can lie on any surface, such as a table, floor, etc. The study concludes that people who had one to five oral sex partners in their lifetime had approximately a doubled risk of throat cancer compared with those who never engaged in this activity, and those with more than five oral sex partners had a percent increased risk. This is because the practice was believed to achieve longevity, and the loss of semen, vaginal, and other bodily liquids is believed to bring about a corresponding loss of vitality. Movements can be slow or fast, regular or erratic, firm or soft, according to the participants' preferences. In Tantric yoga, the same emphasis is placed on the retention and absorption of vital liquids and Sanskrit texts describe how the male semen must not be emitted if the yogi is to avoid falling under law of time and death. In this position she has more control over her body movements and can guide her partner or auto-stimulate against the partner's face. A person who performs cunnilingus may be referred to as a cunnilinguist. Some sex manuals recommend beginning with a gentler, less focused stimulation of the labia and the whole genital area. The study found that 36 percent of the cancer patients had HPV compared to only 1 percent of the healthy control group. Additional common slang terms used are giving lip, lip service , or tipping the velvet ; this last is an expression that novelist Sarah Waters argues that she "plucked from the relative obscurity of Victorian porn". The performing partner may also hum to produce vibration. The incisal edges of the mandibular teeth can be smoothed to minimize the chance of trauma.