preferences for specific sexual practices among female same-sex relationships have also been studied. masters and johnson concluded that vaginal penetration with dildos is rare and lesbians tend to do more overall genital stimulation than direct clitoral stimulation, which is also often the case for heterosexual relationships. concerning oral sex, the common belief that all women who have sex with women engage in cunnilingus contrasts research on the subject. some lesbian or bisexual women dislike oral sex because they do not like the experience or due to psychological or social factors, such as finding it unclean. other lesbian or bisexual women believe it is a necessity or largely defines lesbian sexual activity. lesbian couples are more likely to consider a woman's dislike of cunnilingus as a problem than heterosexual couples are, and it is common for them to seek therapy to overcome inhibitions regarding it.