If performed on oneself, the act is called autofellatio. Fellatio can be sexually arousing for both participants, and may lead to orgasm for the receiving partner. However, the transmission risk for oral sex, especially HIV transmission, is significantly lower than for vaginal or anal sex. Most countries do not have laws that ban the practice of oral sex, though some cultures may consider it taboo. In fellatio the -us is replaced by the -io ; the declension stem ends in -ion- , which gives the suffix the form -ion cf.