LEV229 [This verse]. All physical closeness is forbidden, such as touching the hands of a married woman (although the verse says "close relatives," the prohibition includes a woman married to someone else (see Sifra 18:15 [146]). According to Rabbeinu Yonah, this prohibition is from the Torah, and not Rabbinic; see his Igeres HaTeshuvah 19, and Zeh Hasha'ar on paragraph 138.); "to uncover her nakedness" means to explain that such physical closeness leads to illicit relations.