Many men find anal intercourse more exciting than penile-vaginal intercourse because the anal opening is usually smaller and tighter than the vagina. However, there are some unfortunate individuals called pseudohermaphrodites, whose sex presents an ambiguous appearance. Carpenter stated that this view "dates to the late s, with explicit 'rules' appearing around the turn of the twentieth century, as in marriage manuals defining petting as 'literally every caress known to married couples but does not include complete sexual intercourse. In a clinical review article of heterosexual anal sex, the term anal intercourse is used to refer specifically to penile-anal penetration, and anal sex is used to refer to any form of anal sexual activity. Retrieved 17 February Textbook of biological psychiatry.